,transcrib]'s ,notes3 ,und]scores 80 be=e & aft] a ^w or phrase indicate italics 9 ! orig9al text4 ,equal signs 80 be=e & aft] a ^w or phrase indicate bold 9 ! orig9al text4 ,small capitals h be5 conv]t$ to ,,solid capitals4 ,illu/rations h be5 mov$ s !y d n break up p>agraphs4 ,typographical & punctuation errors h be5 sil5tly correct$4 ,page #da3 8#a1jjj1jjj feet or #cjj1jjj kilometres p] second0 *ang$ to 8#a1jjj1jjj1jjj feet or #cjj1jjj kilometres p] second0 ,,! ,,atom ,,& ,,! ,,bohr ,,!ory ,,( ,,its ,,/ructure ,orig9al ,title3 8,bohr's ,atomteori1 alm5fatteligt frem/illet0 ,translat$ f ! ,dani% by #a ,fell[ ( ! ,am]ican-,sc&9avian ,f\ndation1 #aibc1 & ,,ra*el ,t4 ,,l9dsay ,illu/ration3 ,niels ,bohr ,,! ,,atom ,,& ,,! ,,bohr ,,!ory ,,( ,,its ,,/ructure ,an ,elem5t>y ,pres5tation ,,by ,h4 ,a4 ,,kram]s ,,lectur] ,,at ,,! ,,in/itute ,,( ,,!oretical ,,physics ,,9 ,,! ,,univ]sity ,,( ,,cop5hag5 ,,& ,,helge ,,hol/ ,,libr>ian ,,at ,,! ,,royal ,,te*nical ,,college ,,( ,,cop5hag5 ,,) ,a ,,=eword ,,by ,,sir ,,erne/ ,,ru!r=d1 ,f4,r4,s4 ,illu/ration ,,new ,,york ,,alfr$ ,a4 ,,knopf #aibc ,,pr9t$ ,,9 ,,great ,,brita9 ,,by ,,morrison ,,& ,,gibb ,,ltd41 ,,ed9burgh ,,preface ,at ! close ( ! n9ete5? c5tury & ! beg9n+ ( ! tw5tie?1 our k ( ! activities 9 ! int]ior ( matt] exp]i5c$ a developm5t :i* surpass$ ! bolde/ hopes t c\ld h be5 ent]ta9$ by ! *emi/s & physici/s ( ! n9ete5? c5tury4 ,! smalle/ p>ticles ( *emi/ry1 ! atoms ( ! elem5ts1 :i* hi!rto _h be5 approa*$ m]ely by inductive ?\ght1 n[ became tangible realities1 s to speak1 :i* c\ld be c\nt$ & ^: tracks c\ld be photograph$4 ,a s]ies ( rem>kable exp]im5tal inve/igations1 /imulat$ l>gely by ! ,engli% physici/1 ,j4 ,j4 ,?omson1 _h disclos$ ! exi/5ce ( negatively *>g$ p>ticles1 ! s-call$ electrons1 _/ ! mass ( ! smalle/ atom ( ! kn[n elem5ts4 ,a !ory ( electrons1 bas$ on ,maxwell's classical electrodynamical !ory & develop$ ma9ly ?r\gh ! lab\rs ( ,lor5tz 9 ,holl& & ,l>mor 9 ,engl&1 _h br\ght ! problem ( atomic /ructure into close connection ) ! !ory ( radiation4 ,! exp]im5ts ( ,ru!r=d prov$1 beyond a d\bt1 t atoms 7 compos$ simply ( light1 negative electric p>ticles1 & small heavy1 positive electric p>ticles4 ,! new 8quantum !ory0 ( ,planck 0 prov+ itself v p[]ful 9 ov]com+ grave difficulties 9 ! !ory ( radiation4 ,! "t ?us seem$ ripe = a compreh5sive inve/igation ( ! fundam5tal problem ( physics--! con/itution ( matt]1 & an explanation 9 t]ms ( simple g5]al laws ( ! physical & *emical prop]ties ( ! atoms ( ! elem5ts4 ,dur+ ! fir/ t5 ye>s ( ! new c5tury ! problem 0 attack$ ) great zeal by _m sci5ti/s1 & _m int]e/+ atomic models 7 develop$ & /udi$4 ,b mo/ ( ^! _h m significance = *emi/ry ?an = physics1 & x 0 n until #aiac t ! "w ( ! ,dani% physici/1 ,niels ,bohr1 pav$ ! way = a really physical inve/igation ( ! problem 9 a rem>kable s]ies ( pap]s on ! spectrum & atomic /ructure ( hydrog54 ,! ideas ( ,bohr1 f\nd$ z !y 7 on ! quantum !ory1 7 />tl+ & revolution>y1 b _! imm5se success 9 expla9+ ! facts ( exp]i5ce aft] a "t won = !m ! wide recognition ( ! sci5tific _w1 & /imulat$ "w by o!r inve/igators along simil> l9es4 ,! pa/ decade has witness$ an enorm\s developm5t at ! h&s ( sci5ti/s 9 all p>ts ( ! _w ( ,bohr's orig9al conceptions2 b ?r\gh x all ,bohr has rema9$ ! lead+ _s1 & ! !ory :i*1 at ! pres5t "t1 gives ! mo/ compreh5sive view ( atomic /ructure may1 !re=e1 mo/ prop]ly be> ! "n ( ,bohr4 ,x is ! object ( ?is book to give ! read] a glimpse ( ! fundam5tal conceptions ( ?is !ory1 toge!r ) "s ( ! mo/ significant results x has atta9$4 ,! book is design$ to meet ! ne$s ( ^? :o wi% to keep abrea/ ( mod]n developm5ts 9 sci5ce1 b h nei!r "t nor incl9ation to delve into ! highly ma!matical ab/ract lit]ature 9 :i* ! developm5ts are usually conceal$4 ,x is ) ?is 9 m9d t ! fir/ f\r *apt]s h be5 devot$ to a g5]al survey ( ^? p>ts ( physics & *emi/ry :i* h close connection ) atomic !ory4 ,no attempt has be5 made at a ma!matical developm5t1 & ! physical mean+ ( su* ma!matical =mul z d occur has be5 cle>ly emphasiz$ 9 ! text4 ,x is hop$1 h[ev]1 t ev5 ^? read]s ^: acqua9tance ) atomic !ory is m ?an casual1 w f9d ! book a /imulus to fur!r /udy ( ! ,bohr !ory4 ,"h we wi% to record our be/ ?anks to ,mr4 & ,mrs4 ,l9dsay = ! ability & ! great c>e ) :i* !y h c>ri$ out ! translation f ! ,dani% orig9al4 ,,=eword ,dur+ ! la/ decade !re has be5 a great advance 9 our k ( ! /ructure ( ! atom & ( ! relation betwe5 ! atoms ( ! *emical elem5ts4 ,9 ! lat] /ages1 sci5ce owes mu* to ! rem>kable a*ievem5ts ( ,pr(essor ,niels ,bohr & 8 co-work]s 9 ,cop5hag54 ,= ! fir/ "t1 we h be5 giv5 a consi/5t !ory to expla9 ! arrangem5t & motion ( ! electrons 9 ! out] atom4 ,! !ory ( ,bohr is n only able to acc\nt 9 consid]able detail = ! v>iation 9 ! prop]ties ( ! elem5ts exemplifi$ by ! p]iodic law1 b also = ! ma9 features ( ! spectra1 bo? ,x-ray & optical1 %[n by all elem5ts4 ,?is volume1 writt5 by ,dr4 ,kram]s & ,mr4 ,hol/1 gives a simple & int]e/+ acc\nt ( our k ( atomic /ructure1 ) special ref]5ce to ! "w ( ,pr(essor ,bohr4 ,dr4 ,kram]s is 9 an especially =tunate position to give a fir/-h& acc\nt ( ?is subject1 = he has be5 a valu$ assi/ant to ,pr(essor ,bohr 9 develop+ 8 !ories1 & has himself made important orig9al contributions to our k 9 ?is bran* ( inquiry4 ,i c confid5tly recomm5d ?is book to ,engli% read]s z a cle>ly writt5 & accurate acc\nt ( ! developm5t ( our ideas on atomic /ructure4 ,x is writt5 9 simple language1 & ! ess5tial ideas are expla9$ )\t ma!matical calculations4 ,?is book %\ld prove attractive n only to ! g5]al sci5tific read]1 b also to ! /ud5t :o wi%es to ga9 a broad g5]al idea ( ?is subject be=e ent]+ into ! details ( ! ma!matical !ory4 ,e4 ,,ru!r=d4 ,,cav5di% ,,laboratory1 ,,cambridge1 #h? ,octob] #aibc4 ,,cont5ts ,,page ,,preface vii ,,=eword xi ,,*ap4 ,i4 ,,atoms ,,& ,,molecules #a ,,ii4 ,,light ,,waves ,,& ,,! ,,spectrum #cd ,,iii4 ,,ions ,,& ,,electrons #fa ,,iv4 ,,! ,,nucle> ,,atom #hc ,v4 ,,! ,,bohr ,,!ory ,,( ,,! ,,hydrog5 ,,spectrum #aje ,,vi4 ,,v>i\s ,,applications ,,( ,,! ,,bohr ,,!ory #aec ,,vii4 ,,atomic ,,/ructure ,,& ,,! ,,*emical ,,prop]ties ,,( ,,! ,,elem5ts #ahj ,,int]pretation ,,( ,,symbols ,,& ,,physical ,,con/ants #bji ,,col\r$ ,,plates ,,plate ,i4 ,,spectrum ,,plates ,,accord+ ,,to ,,! ,,orig9al ,,draw+s ,,( ,,buns5 ,,& ,,kir*h(f ,at end ,,ii4 ,,pr9cipal ,,features ,,( ,,atomic ,,/ructure ,,9 ,,"s ,,( ,,! ,,elem5ts--,,atomic ,,/ructure ,,( ,,radium ,at end ,,! ,,atom ,,& ,,! ,,bohr ,,!ory ,,( ,,its ,,/ructure ,,*apt] ,i ,,atoms ,,& ,,molecules ,introduction4 ,z e>ly z #djj ,b4,c4 ! ,greek philosoph]1 ,democritus1 taught t ! _w consi/$ ( empty space & an inf9ite numb] ( small invisible p>ticles4 ,^! p>ticles1 diff]+ 9 =m & magnitude1 by _! arrangem5ts & movem5ts1 by _! unions & disunions1 caus$ ! exi/5ce ( physical bodies ) diff]5t *>act]i/ics1 & also produc$ ! obs]v$ v>iations 9 ^! bodies4 ,?is !ory1 :i* no d\bt ant$at$ ,democritus1 lat] became kn[n z ! ,atomic ,!ory1 s9ce ! p>ticles 7 call$ atoms1 i4e4 ! 8indivisible40 ,b ! atomic conception 0 n ! g5]ally accept$ "o 9 antiquity4 ,ari/otle 7#chd-cbb ,b4,c47 0 n an atomi/1 & d5i$ ! exi/5ce ( discont9u\s matt]2 8 philosophy _h a trem5d\s influ5ce ^u ! ideas ( ! anci5ts1 & ev5 ^u ! beliefs ( ! ,middle ,ages4 ,x mu/ be confess$ t 8 conception ( ! cont9uity ( matt] seem$ to agree be/ ) exp]im5t1 because ( ! app>5t homog5eity ( physical sub/ances su* z metal1 glass1 wat] & air4 ,b ev5 ?is app>5t homog5eity c\ld n be consid]$ entirely inconsi/5t ) ! atomic !ory1 =1 accord+ to ! latt]1 ! atoms 7 s small z to be invisible4 ,moreov]1 ! atomic !ory left ! way op5 = a m complete und]/&+ ( ! prop]ties ( matt]4 ,?us :5 air 0 compress$ & !reaft] all[$ to exp&1 or :5 salt 0 dissolv$ 9 wat] produc+ an app>5tly new homog5e\s liquid1 salt wat]1 or :5 silv] 0 melt$ by heat1 or light *ang$ col\r on pass+ ?r\gh w9e1 x 0 cle> t some?+ _h happ5$ 9 ! int]ior ( ! sub/ances 9 "q4 ,b complete homog5eity is synonym\s ) inactivity4 ,h[ is x possible to obta9 a def9ite idea ( ! inn] activity ly+ at ! bottom ( ^! *anges ( /ate1 if we d n ?9k ( ! ph5om5on z an int]play betwe5 ! diff]5t p>ts ( ! app>5tly homog5e\s matt]8 ,?us1 9 ! examples above1 ! decrease 9 ! volume ( ! air might be consid]$ z due to ! p>ticles draw+ ne>] to ea* o!r2 ! dissolv+ ( salt 9 wat] might be look$ ^u z ! movem5t ( ! salt p>ticles 9 betwe5 ! wat] p>ticles & ! comb9ation ( ! two k9ds2 ! melt+ ( silv] might naturally appe> to be due to ! loos5+ ( bonds betwe5 ! individual silv] p>ticles4 ,! atomic !ory _h ?us a s\nd physical basis1 & prov$ p>ticul>ly attractive to ^? philosoph]s :o tri$ to expla9 ! my/]i\s activity ( matt] 9 t]ms ( exact measurem5ts4 ,! atomic hypo!sis 0 nev] completely ov]?r[n1 be+ support$ aft] ! "t ( ,ari/otle by ,epicurus 7c4 #cjj ,b4,c471 :o introduc$ ! t]m 8atom10 & by ! ,lat9 poet1 ,lucretius 7c4 #ge ,b4,c47 9 8 ,de ,r]um ,natura4 ,ev5 9 ! ,middle ,ages x 0 support$ by m5 ( indep5d5t ?\ght1 su* z ,ni*olas ( ,autrucia1 :o assum$ t all natural activities 7 due to unions or disunions ( atoms4 ,x is int]e/+ to note t 9 #acdh he 0 =c$ to retract ?is h]esy4 ,) ! impetus giv5 to ! new physics by ,galileo 7#afjj7 ! atomic view gradually spread1 sometimes explicitly /at$ z atomic !ory1 sometimes z a backgr\nd = ! ideas ( individual philosoph]s4 ,v>i\s inve/igators develop$ compreh5sive atomic !ories 9 :i* !y attempt$ to expla9 ne>ly ev]y?+ f purely arbitr>y hypo!ses2 !y occasionally arriv$ at v curi\s & amus+ conceptions4 ,= example1 ab\t #afej ! ,fr5*man1 ,pi]re ,gass5di1 foll[+ "s ( ! anci5t atomi/s1 expla9$ ! solidity ( bodies by assum+ a hook-l =m ( atom s t ! v>i\s atoms 9 a solid body c\ld be hook$ toge!r4 ,he ?\ght ( fro/ z an elem5t ) tetrah$ral atoms1 t is1 atoms ) f\r plane faces & ) f\r v]tices ea*2 ! v]tices produc$ ! *>act]i/ic prick+ s5sation 9 ! sk94 ,a mu* m ?or\gh treatm5t ( ! atomic !ory 0 giv5 by ,boscovi* 7#aggj74 ,he saw t x 0 unnecess>y to conceive ( ! atoms z sph]es1 cubes1 or o!r %>ply def9$ physical bodies2 he consid]$ !m simply z po9ts 9 space1 ma!matical po9ts ) ! additional prop]ty ( be+ c5tres ( =ce4 ,he assum$ t any two atoms influ5c$ ea* o!r ) a =ce :i* v>i$1 accord+ to a complicat$ =mula1 ) ! di/ance betwe5 ! c5tres4 ,b ! "t 0 h>dly ripe = su* a !ory1 inspir$ z x evid5tly 0 by ,newton's tea*+s ab\t ! gravitational =ces betwe5 ! bodies ( ! univ]se4 ,inde$ !re 7 no physical exp]im5ts ^: results c\ld1 ) c]ta9ty1 be assum$ to express ! prop]ties ( ! individual atoms4 ,! ,atomic ,!ory & ,*emi/ry4 ,illu/ration3 ,,fig4 #a4--,! f\r elem5ts & ! f\r fundam5tal *>act]i/ics4 ,9 ! meantime atomic inve/igations ( a v diff]5t nature _h be5 influ5c+ ! new sci5ce ( *emi/ry1 9 :i* ! atomic !ory 0 lat] to prove itself extraord9>ily fruitful4 ,x 0 p>ticul>ly un=tunate t 9 *emi/ry1 conc]n$ z x is ) ! inn] activities ( ! elem5ts1 ,ari/otle's philosophy 0 long ! prevail+ "o4 ,he adopt$ & develop$ ! fam\s !ory ( ! f\r 8elem5ts10 namely1 ! dry & cold e>?1 ! cold & damp wat]1 ! damp & w>m air1 ! w>m & dry fire4 ,^! 8elem5ts0 mu/ n be confus$ ) ! *emical elem5ts kn[n at ! pres5t day2 !y 7 m]ely repres5tatives ( ! diff]5t consi/5t comb9ations ( ! f\r fundam5tal qualities1 dryness & wetness1 heat & cold4 ,f ! symmetry 9 ! sy/em ^! 7 suppos$ to be ! pr9ciples by means ( :i* all ! prop]ties ( matt] c\ld be expla9$4 ,nei!r ! f\r 8elem5ts0 nor ! f\r fundam5tal qualities c\ld be cle>ly def9$2 !y 7 vague ideas to be discuss$ 9 long dialectic treatises1 b 7 f\nd$ ^u no physical quantities :i* c\ld be measur$4 ,a sy/em ( *emi/ry :i* _h its !oretical f\ndations 9 ! ,greek elem5tal conceptions naturally _h to "w 9 ! d>k4 ,und\bt$ly ?is unc]ta9ty contribut$ to ! relatively insignificant results ( all ! lab\r exp5d$ 9 ! ,middle ,ages on *emical exp]im5ts1 _m ( :i* _h to d ) ! attempt to transmute ! base metals into gold4 ,naturally !re 7 _m important contributions to *emi/ry1 & ! !ories 7 *ang$ & develop$ 9 _m ways 9 ! c\rse ( "t4 ,! al*emi/s ( ! ,middle ,ages ?\ght t metal consi/$ only ( sulphur & quicksilv]2 b ! int]pretation ( ?is idea 0 influ5c$ by ! ,greek elem5tal !ory :i* 0 ma9ta9$ at ! same "t2 ?us ^! new metal 8elem5ts0 7 consid]$ by _m m]ely z ! expressions ( c]ta9 aspects ( ! metallic *>act]i/ics1 r ?an z def9ite sub/ances1 id5tical ) ! elem5ts be>+ ^! names4 ,x is1 h[ev]1 necess>y to gu>d aga9/ attribut+ to a s+le conception too great influ5ce on ! hi/orical developm5t ( ! *emical & physical sci5ces4 ,t ! gr[? ( ! latt] 0 h9d]$ = s long a "t 0 due m to ! uncritical fai? 9 au?ority & to ! :ole *>act]i/ic psy*ological po9t ( view :i* gov]n$ ,we/]n ?\ght 9 ! c5turies prec$+ ! ,r5aissance4 ,rob]t ,boyle 7#afbg-afia7 is "o ( ! m5 to :om great hon\r is due = bru%+ aside ! old ideas ab\t ! elem5ts :i* _h orig9at$ 9 obscure philosophical m$itations4 ,to him an elem5t 0 simply a sub/ance :i* by no me?od c\ld be sep>at$ into o!r sub/ances1 b :i* c\ld unite ) o!r elem5ts to =m *emical comp\nds possess+ v diff]5t *>act]i/ics1 includ+ t ( be+ decomposable into _! con/itu5t elem5ts4 ,und\bt$ly ,boyle's cle> conception ( ?is matt] 0 connect$ ) 8 repres5tation ( matt] z ( an atomic nature4 ,accord+ to ! atomic conception1 ! *emical processes d n dep5d ^u *anges )9 ! elem5t itself1 b r 9 ! union or disunion ( ! con/itu5t atoms4 ,?us :5 iron sulphide is produc$ by heat+ iron & sulphur toge!r1 accord+ to ?is conception1 ! iron atoms & ! sulphur atoms comb9e 9 su* a way t ea* iron atom l9ks itself ) a sulphur atom4 ,!re is !n a def9ite mean+ 9 ! /atem5t t iron sulphide consi/s ( iron & sulphur1 & t ^! two sub/ances are bo? repres5t$ 9 ! new sub/ance4 ,!re is also a def9ite mean+1 = in/ance1 9 ! /atem5t t iron is an elem5t1 namely1 t by no kn[n means c ! iron be brok5 d[n into diff]5t k9ds ( atoms :i* c be reunit$ to produce a sub/ance diff]5t f iron4 ,! cl>ity :i* ! atomic int]pretation gave to ! conception ( *emical elem5ts & comp\nds 0 surely mo/ useful to *emical rese>* 9 ! foll[+ ye>s2 b be=e ! atomic !ory c\ld play a really great rle 9 *emi/ry1 x _h to und]go consid]able developm5t4 ,9 ! "t ( ,boyle1 & ev5 lat]1 !re 0 /ill unc]ta9ty z to :i* sub/ances 7 ! elem5ts4 ,?us1 wat] 0 g5]ally consid]$ z an elem5t4 ,accord+ to ! s-call$ phlogi/on !ory develop$ by ! ,g]man ,/ahl 7#affj-agcd71 a !ory :i* prevail$ 9 *emi/ry = _m ye>s1 ! metals 7 *emical comp\nds consi/+ ( a gase\s sub/ance1 phlogi/on1 :i* 0 driv5 (f :5 ! metals 7 heat$ 9 air1 & ! metallic oxide :i* 0 left beh9d4 ,x 0 n until ! latt] half ( ! eighte5? c5tury t ! f\ndation 0 laid = ! new *emical sci5ce by a s]ies ( discov]ies & rese>*es c>ri$ on by ! ,sw$i% sci5ti/ ,s*eele1 ! ,engli%m5 ,prie/ley & ,cav5di%1 & p>ticul>ly by ! ,fr5*man ,lavoisi]4 ,x 0 !n discov]$ t wat] is a *emical comp\nd ( ! gase\s elem5ts oxyg5 & hydrog51 t air is pr9cipally a mixture 7n a comp\nd7 ( oxyg5 & nitrog51 t combu/ion is a *emical process 9 :i* "s sub/ance is unit$ ) oxyg51 t metals are elem5ts1 :ile metallic oxides1 on ! o!r h&1 are comp\nds ( metal & oxyg51 etc4 ,( special significance = ! atomic !ory 0 ! fact t ,lavoisi] made weigh+ "o ( ! mo/ p[]ful tools ( sci5tific *emi/ry4 ,weigh+ _h inde$ be5 us$ previ\sly 9 *emical exp]im5ts1 b ! exp]im5t]s _h be5 satisfi$ ) v crude precision1 & ! results _h little influ5ce on *emical !ory4 ,= example1 ! phlogi/on !ory 0 ma9ta9$ 9 spite ( ! fact t x 0 well kn[n t metallic oxide weigh$ m ?an ! metal f :i* x 0 obta9$4 ,lavoisi] n[ %[$1 by v c>eful weigh+s1 t *emical comb9ations or decompositions c nev] *ange ! total weight ( ! sub/ances involv$2 a giv5 quantity ( metallic oxide weighs j z mu* z ! metal & ! oxyg5 tak5 individually1 or vice v]sa4 ,f ! po9t ( view ( ! atomic !ory1 ?is obvi\sly means t ! weight ( individual atoms is n *ang$ 9 ! comb9ations ( atoms :i* occur 9 ! *emical processes4 ,9 o!r words1 ! weight ( an atom is an inv>iable quantity4 ,"h1 !n1 we h ! fir/ prop]ty ( ! atom itself to be e/abli%$ by exp]im5t--a prop]ty1 inde$1 :i* mo/ atomi/s _h already tacitly assum$4 ,moreov]1 by ! practice ( weigh+ x 0 det]m9$ t to e *emical comb9ation !re corresponds a def9ite weight ratio among ! con/itu5t p>ts4 ,?is also _h be5 previ\sly accept$ by mo/ *emi/s z highly probable2 b x mu/ be admitt$ t ! law at "o "t 0 assail$ f sev]al sides4 ,9 comp>+ ! weight ratios 9 diff]5t *emical comp\nds c]ta9 rules 71 9 ! meantime1 obta9$4 ,9 _m ways ! mo/ important ( ^!1 ! s-call$ law ( multiple proportions1 0 enunciat$ 9 ! beg9n+ ( ! la/ c5tury by ! ,engli%man1 ,john ,dalton4 ,z an example ( ?is law we may take two comp\nds ( c>bon & hydrog5 call$ me?ane or m>% gas & e?yl5e1 9 :i* ! quantities ( hydrog5 comp\nd$ ) ! same quantity ( c>bon are z two is to "o4 ,ano!r example may be se5 9 ! comp\nds ( c>bon & oxyg54 ,9 ! two comp\nds ( c>bon & oxyg51 c>bon monoxide & c>bon dioxide1 ! weight ratios betwe5 ! c>bon & oxyg5 are respectively z ?ree to f\r & ?ree to eight4 ,a def9ite quantity ( c>bon has ?us 9 c>bon dioxide comb9$ ) j twice z mu* oxyg5 z 9 c>bon monoxide4 ,no less ?an five oxyg5 comp\nds ) nitrog5 are kn[n1 :]e ) a giv5 quantity ( nitrog5 ! oxyg5 is comb9$ 9 ratios ( "o1 two1 ?ree1 f\r & five4 ,^! simple numb] relations c be expla9$ v easily by ! atomic !ory1 by assum+1 fir/1 t all atoms ( ! same elem5t h ! same weight2 & second1 t 9 a *emical comb9ation betwe5 two elem5ts ! atoms comb9e to =m an atomic gr\p *>act]i/ic ( ! comp\nd 9 "q--a comp\nd atom1 z ,dalton call$ x1 or a molecule1 z ! atomic gr\p is n[ call$4 ,^! molecules consi/ ( comp>atively few atoms1 z1 = example1 "o ( ea* k9d1 or "o ( "o k9d & two1 ?ree or f\r ( ano!r1 or two ( "o k9d & ?ree or f\r ( ano!r1 etc4 ,:5 ?ree elem5ts are involv$ 9 a *emical comp\nd ! molecule mu/ conta9 at lea/ ?ree atoms1 b !re may be f\r1 five1 six or m4 ,! law ( multiple proportions ?us takes on a m complicat$ "*1 b x rema9s app>5t ev5 9 ?is case4 ,:5 ,dalton 9 ! beg9n+ ( la/ c5tury =mulat$ ! !ory ( ! =mation ( *emical comp\nds f ! atoms ( ! elem5ts1 he at once turn$ atomic !ory into ! pa? ( m practical rese>*1 & x 0 soon evid5t t *emical rese>* _h !n obta9$ a valuable tool4 ,x may be said t ,dalton's atomic !ory is ! firm f\ndation ^u :i* mod]n *emi/ry is built4 ,illu/ration ,illu/ration ,illu/ration ,illu/ration3 ,,fig4 #b4--,repres5tation ( a "p ( ,dalton's atomic table 7( #ahjh7 :]e ! atom ( ea* elem5t has its own symbol1 & *emical comp\nds are indicat$ by ! union ( ! atoms ( ! elem5ts into gr\ps by #b1 #c1 #d 444 7b9>y1 t]n>y1 quat]n>y 444 atoms74 ,bel[ are giv5 ! designations ( ! diff]5t atoms1 & 9 p>5!ses ! atomic weight giv5 by ,dalton ) t ( hydrog5 z unity & ! designations ( ! indicat$ atomic gr\ps4 ,atoms ( ! ,elem5ts4--#a4 ,hydrog5 7#a72 #b4 ,azote 7#e72 #c4 ,c>bon 7#e72 #d4 ,oxyg5 7#g72 #e4 ,phosphorus 7#i72 #f4 ,sulphur 7#ac72 #g4 ,magnesia 7#bj72 #h4 ,lime 7#bc72 #i4 ,soda 7#bh72 #aj4 ,pota% 7#db72 #aa4 ,/rontites 7#df72 #ab4 ,b>ytes 7#fh72 #ac4 ,iron 7#ch72 #ad4 ,z9c 7#ef72 #ae4 ,copp] 7#ef72 #af4 ,lead 7#ie72 #ag4 ,silv] 7#ajj72 #ah4 ,plat9a 7#ajj72 #ai4 ,gold 7#adj72 #bj4 ,m]cury 7#afg74 ,*emical ,comp\nds4--#ba4 ,wat]2 #bb4 ,ammonia2 #bc4 #bf4 #bg4 & #cj4 ,oxyg5 comp\nds ( ,azote2 #bd4 #bi4 & #cc4 ,hydrog5 comp\nds ( ,c>bon2 #be4 ,c>bon monoxide2 #bh4 ,c>bon dioxide2 #ca4 ,sulphuric acid2 #cb4 ,hydro-sulphuric acid4 ,:ile ,dalton's !ory c\ld n give in=mation ab\t ! absolute weights 9 grams ( ! atoms ( v>i\s elem5ts1 x c\ld say some?+ ab\t ! relative atomic weights1 i4e41 ! ratios ( ! weights ( ! diff]5t k9ds ( atoms1 al?\gh x is true t ^! ratios c\ld n always be det]m9$ ) c]ta9ty4 ,if1 = example1 ! ratio betwe5 ! oxyg5 & hydrog5 9 wat] is f\nd to be z eight to "o1 !n ! weight ratio betwe5 ! oxyg5 atom & ! hydrog5 atom w be z eight to "o1 if ! wat] molecule is compos$ ( "o oxyg5 atom & "o hydrog5 atom 7z ,dalton suppos$1 see ,fig4 #b74 ,b x w be z sixte5 to "o1 if ! wat] molecule is compos$ ( "o oxyg5 & two hydrog5 atoms 7z we n[ "k to be ! case74 ,on ! o!r h&1 a ratio ( sev5 to "o w be compatible ) ! exp]im5tal ratio ( eight to "o only if we assume t ! wat] molecule consi/s ( fifte5 atoms1 eight ( oxyg5 & sev5 ( hydrog51 a v improbable hypo!sis4 ,9 ano!r case let u comp>e ! quantities ( oxyg5 & ( hydrog5 :i* are comp\nd$ ) ! same quantities ( c>bon 9 ! two sub/ances1 c>bon monoxide & me?ane respectively4 ,on ! assumption t ! molecules 9 "q h a simple /ructure1 we c draw conclusions ab\t ! ratio ( ! atomic weights ( hydrog5 & oxyg54 ,n[1 if a ratio su* z sev5 to "o or f\rte5 to "o is obta9$ :ile ! analysis ( wat] gives eight to "o or sixte5 to "o1 !n ei!r ! /ructure ( ! molecule is m complicat$ ?an 0 assum$1 or ! analyses mu/ be improv$ by m c>eful exp]im5ts4 ,we c ?us und]/& t ! atomic !ory c s]ve z a controll+ influ5ce on ! analysis ( *emical comp\nds4 ,9 ord] to *oose betwe5 ! diff]5t possible ratios ( atomic weights1 = example1 ! eight to "o or ! sixte5 to "o 9 ! case ( oxyg5 & hydrog51 ,dalton _h to make c]ta9 arbitr>y assumptions4 ,! fir/ ( ^! is t two elem5ts ( :i* only "o comp\nd is kn[n appe> ) b "o atom ea* 9 a molecule4 ,p>tly on acc\nt ( ?is assumption & p>tly on acc\nt ( ! incomplet5ess ( 8 analyses1 ,dalton's values ( ! ratios ( ! atomic weights ( ! atoms & 8 pictures ( ! /ructure ( molecules diff] f ^? ( ! pres5t day1 z is obvi\s f ,fig4 #b4 ,a mu* firm] f\ndation = ! *oice made appe>s lat] 9 ! ,avogadro ,law2 />t+ ) ! fact t diff]5t gases %[ great simil>ity 9 _! physical conduct--= in/ance1 all exp& by an increase ( ( _! volume ) an increase 9 temp]ature f #j ,c4 to #a ,c4--! ,italian1 ,avogadro1 9 #ahaa1 put =w>d ! hypo!sis t equal volumes ( all gases at ! same temp]ature & pressure conta9 equal numb]s ( molecules4 ,a few examples suffice to %[ ! usefulness ( ?is rule4 ,:5 "o volume ( ! gas *lor9e unites ) "o volume ( hydrog5 !re result two volumes ( ! gas1 hydrog5 *loride1 at ! same temp]ature & pressure4 ,accord+ to ,avogadro's ,law "o molecule ( *lor9e & "o molecule ( hydrog5 unite to become two molecules ( hydrog5 *loride1 & s9ce ea* ( ^! two molecules mu/ conta9 at lea/ "o atom ( hydrog5 & "o atom ( *lor9e1 x foll[s t "o molecule ( *lor9e mu/ conta9 two atoms ( *lor9e & t "o molecule ( hydrog5 mu/ conta9 two atoms ( hydrog54 ,f ?is "o c see t ev5 9 ! elem5ts ! atoms are unit$ into molecules4 ,x is n[ well e/abli%$ t mo/ elem5ts h diatomic molecules1 ?\gh "s1 includ+ m]cury & _m o!r metals1 are monatomic4 ,:5 oxyg5 & hydrog5 unite to =m wat]1 "o litre ( oxyg5 & two litres ( hydrog5 produce two litres ( wat] vap\r at same temp]ature & pressure4 ,accord+ly1 "o molecule ( oxyg5 & two molecules ( hydrog5 =m two molecules ( wat]4 ,if ! oxyg5 molecule is diatomic l ! hydrog51 !n "o molecule ( wat] conta9s "o atom ( oxyg5 & two atoms ( hydrog54 ,s9ce ! weight ratio betwe5 ! oxyg5 & hydrog5 9 wat] is eight to "o1 ! atomic weight ( oxyg5 mu/ be sixte5 times t ( hydrog54 ,?r\gh su* consid]ations1 support$ by c]ta9 o!r rules1 x has gradually prov$ possible to obta9 reliable figures = ! ratios betwe5 ! atomic weights ( all kn[n elem5ts & ! atomic weight ( hydrog54 ,= conv5i5ce x 0 cu/om>y to assign ! numb] #a to ! latt] & to call ! ratio betwe5 ! weight ( ! atom ( a giv5 elem5t & ! weight ( ! hydrog5 atom ! atomic weight ( ! elem5t 9 "q4 ,?us ! atomic weight ( oxyg5 is #af1 t ( c>bon #ab1 because "o c>bon atom weighs z mu* z #ab hydrog5 atoms4 ,nitrog5 has ! atomic weight #ad1 sulphur #cb1 copp] #fc4f1 etc4 ,a summ>y ( ! *emical prop]ties & *emical comp\nds 0 greatly facilitat$ by ! symbolic sy/em initiat$ by ! ,sw$i% *emi/1 ,b]zelius4 ,9 ?is sy/em ! initial ( ! ,lat9 "n ( ! elem5t 7sometimes ) "o o!r lett] f ! ,lat9 "n7 is made to indicate ! elem5t itself1 an atom ( ! elem5t1 & its atomic weight ) respect to hydrog5 z unity1 :ile a small subscript to ! initial designates ! numb] ( atoms to be us$4 ,= example1 9 ! *emical =mula = sulphuric acid1 ,h,,s1 ! symbolic =mula means t ?is sub/ance is a *emical comp\nd ( hydrog51 sulphur & oxyg51 t ! acid molecule consi/s ( two atoms ( hydrog51 "o atom ( sulphur & f\r atoms ( oxyg51 & t ! weight ratios betwe5 ! ?ree con/itu5t p>ts is z #ba #b to #cb to #daf #fd1 or z #a3af3cb4 ,to say t ! *emical =mula ( z9c *loride is ,zn,cl means t ! z9c *loride molecule consi/s ( "o atom ( z9c & two atoms ( *lor9e4 ,fur!rmore ! *anges :i* take place 9 a *emical process may be indicat$ 9 a v simple way4 ,?us ! decomposition ( wat] into hydrog5 & oxyg5 may be repres5t$ by ! s-call$ *emical 8equation0 #b;,h,o #b;,h,o1 :]e ,h & ,o signify ! molecules ( hydrog5 & oxyg5 respectively4 ,conv]sely1 ! comb9ation ( hydrog5 & oxyg5 to =m wat] w be giv5 by ! equation #b;,h,o #b;,h,o4 ,z a consequ5ce ( ! developm5t ( ! atomic !ory ! atoms ( ! elem5ts became1 s to speak1 ! build+ /ones ( :i* ! elem5ts & ! *emical comp\nds are built4 ,x c also be said t ! atoms are ! smalle/ p>ticles :i* ! *emi/s reckon ) 9 ! *emical processes1 b x does n foll[ f ! !ory t ^! build+ /ones 9 !mselves are indivisible4 ,! !ory leaves ! way op5 to ! idea t !y are compos$ ( small] p>ts4 ,a belief f\nd$ on su* an idea 0 inde$ enunciat$ by ! ,engli%man1 ,pr\t1 a %ort "t aft] ,dalton _h develop$ 8 atomic !ory4 ,pr\t assum$ t ! hydrog5 atoms 7 ! fundam5tal ones1 & t ! atoms ( ! o!r elem5ts consi/$ ( a small] or l>g] numb] ( ! atoms ( hydrog54 ,?is might expla9 ! fact t )9 ! limits ( exp]im5tal error1 _m atomic weights seem$ to be integral multiples ( t ( hydrog5--#af = oxyg51 #ad = nitrog51 & #ab = c>bon1 etc4 ,?is l$ to ! possibility t ! same might hold = all elem5ts1 & ?is hypo!sis gave impetus to v c>eful det]m9ations ( atomic weights4 ,^!1 h[ev]1 %[$ t ! assumption ( ! integral multiples c\ld n be v]ifi$4 ,x !re=e seem$ z if ,pr\t's hypo!sis w\ld h to be giv5 up4 ,x has1 h[ev]1 rec5tly come into its own aga91 al?\gh ! situation is m complicat$ ?an ,pr\t _h imag9$ 7see p4 #ig74 ,dalton's atomic !ory gave no in=mation ab\t ! atoms except t ! atoms ( ea* elem5t _h a def9ite con/ant weight1 & t !y c\ld comb9e to =m molecules 9 c]ta9 simple ratios4 ,:at ! =ces are :i* unite !m into su* comb9ations1 & :y !y pref] c]ta9 unions to o!rs1 7 v p]plex+ problems1 :i* c\ld only be solv$ :5 *emical & physical rese>* _h collect$ a great mass ( in=mation z a sur] s\rce ( speculation4 ,f ! k ( atomic weights x 0 easy to calculate :at weight ratios might be f\nd to exi/ 9 *emical comp\nds1 ! molecules ( :i* consi/$ ( simple atomic comb9ations4 ,?us _m comp\nds :i* 7 lat] produc$ 9 ! laboratory 7 fir/ pr$ict$ !oretically1 b only a small "p ( ! total numb] ( possible comp\nds 7correspond+ to simple atomic comb9ations7 c\ld actually be produc$4 ,cle>ly x 0 "o ( ! greate/ problems ( *emi/ry to f9d ! laws gov]n+ ^! cases4 ,x _h e>ly be5 kn[n t ! elem5ts seem$ to fall into two gr\ps1 *>act]iz$ by c]ta9 fundam5tal diff]5ces1 ! metals & ! metalloids4 ,9 addition1 !re 7 recogniz$ two v important gr\ps ( *emical comp\nds1 i4e4 acids & bases1 possess+ ! prop]ty ( neutraliz+ ea* o!r to =m a ?ird gr\p ( comp\nds1 ! s-call$ salts4 ,! ph5om5on call$ electrolysis1 9 :i* an electric curr5t sep>ates a dissolv$ salt or an acid into two p>ts :i* are c>ri$ respectively ) & aga9/ ! direction ( ! curr5t1 indicates /rongly t ! =ces hold+ ! atoms toge!r 9 ! molecule are ( an electrical nature1 i4e4 ( ! same nature z ^? =ces :i* br+ toge!r bodies ( opposite electrical *>ges4 ,"o is l$ to d5ote all metals z electropositive & all metalloids z electronegative1 :i* means t 9 a comp\nd consi/+ ( a metal & a metalloid ! metal appe>s ) a positive *>ge & ! metalloid ) a negative *>ge4 ,! *emi/ ,b]zelius did a great deal to develop electrical !ories = *emical processes4 ,great difficulties1 h[ev]1 7 enc\nt]$1 "s prov+ = ! "t be+ insurm\ntable4 ,su* a difficulty1 = example1 is ! circum/ance t two atoms ( ! same k9d 7l two hydrog5 atoms7 c unite into a diatomic molecule1 al?\gh "o might expect !m to be simil>ly electrifi$ & to repel r ?an attract ea* o!r4 ,ano!r circum/ance play+ a v important "p 9 det]m9+ ! *emical comp\nds :i* are possible1 is ! consid]ation ( :at is call$ val5ce4 ,z m5tion$ above1 "o atom ( oxyg5 comb9es ) two atoms ( hydrog5 to =m wat]1 :ile "o atom ( *lor9e comb9es ) b "o atom ( hydrog5 to =m hydrog5 *loride4 ,! oxyg5 atom ?us seems to be 8equival5t0 to two hydrog5 atoms or two *lor9e atoms1 :ile "o *lor9e atom is 8equival5t0 to "o hydrog5 atom4 ,! atoms ( hydrog5 & *lor9e are = ?is reason call$ monoval5t1 :ile t ( oxyg5 is call$ dival5t4 ,aga9 an acid is a *emical comp\nd conta9+ hydrog51 9 :i* ! hydrog5 c be replac$ by a metal to produce a metallic salt4 ,?us1 :5 z9c is dissolv$ by sulphuric acid to =m hydrog5 & ! salt z9c sulphate1 ! hydrog5 ( ! acid is replac$ by ! z9c & ! *emical *ange may be express$ by ! =mula ,zn,h,,s ,h,zn,s,o ,9 ?is1 "o atom ( z9c *anges place ) two atoms ( hydrog54 ,! z9c atom is !re=e dival5t4 ,?is is consi/5t ) ! fact t "o z9c atom w comb9e ) "o oxyg5 atom to =m z9c oxide4 ,to take ano!r example1 if silv] is dissolv$ 9 nitric acid1 "o atom ( silv] is ex*ang$ = "o atom ( hydrog54 ,silv]1 !re=e1 is monoval5t1 & we %\ld expect t "o atom ( oxyg5 w\ld unite ) two atoms ( silv]4 ,"s elem5ts are trival5t1 z1 = example1 nitrog51 :i* comb9es ) hydrog5 to =m ammonia1 ,,nh2 o!rs1 aga91 are tetraval5t1 su* z c>bon1 :i* unites ) hydrog5 to =m m>% gas ,,*1 & ) oxyg5 to =m c>bon dioxide ,,co4 ,a val5ce great] ?an sev5 or eight has n be5 f\nd 9 any elem5t4 ,illu/ration3 ,,fig4 #c4--,r\gh illu/rations ( ! val5ces ( ! elem5ts4 ,a4 ,hydrog5 *loride 7,h,cl72 ,b4 ,wat] 7,h,o72 ,c4 ,me?ane 7,,*72 ,d4 ,e?yl5e 7,c,h74 ,if we consid] ! matt] r r\ghly & m or less z ,gass5di did1 we c expla9 ! concept ( val5ce by assum+ t ! atoms possess hooks2 ?us hydrog5 & *lor9e are ea* furni%$ ) "o hook1 oxyg5 & z9c ) two hooks1 nitrog5 ) ?ree hooks1 etc4 ,:5 a hydrog5 atom & a *lor9e atom are hook$ toge!r1 !re are no free hooks left1 & consequ5tly ! comp\nd is said to be saturat$4 ,:5 "o hydrog5 atom is hook$ into ea* ( ! hooks ( an oxyg5 or c>bon atom ! saturation is also complete 7see ,fig4 #c1 ,a1 ,b1 ,c74 ,! matt] is n s simple z ?is1 h[ev]1 s9ce ! same elem5t c (t5 appe> ) diff]5t val5ces4 ,iron may be dival5t1 trival5t or hexaval5t 9 diff]5t comp\nds4 ,9 _m cases1 h[ev]1 :]e an exam9ation ( ! weight ratios seems to %[ t an elem5t has *ang$ its val5ce1 ?is is n really true4 ,x 0 m5tion$ previ\sly t c>bon =ms ano!r comp\nd ) hydrog5 9 addition to ,,*1 namely1 e?yl5e1 conta9+ half z mu* hydrog5 9 proportion to ! same am\nt ( c>bon4 ,) ! aid ( ,avogadro's ,law1 x is f\nd t ! e?yl5e molecule is n ,,* b ,c,h4 ,?us we c say t ! two c>bon atoms 9 ! molecule are held toge!r by two pairs ( hooks1 & consequ5tly ! comp\nd c be express$ by ! =mula ,h-,c-,h ,h-,c-,h :]e ! da%es correspond to hooks 7cf4 ,fig4 #c1 ,d74 ,su* a =mula is call$ a /ructural =mula4 ,ev5 if we are n all[$ to ?9k ( ! atoms 9 ! molecules z held toge!r by hooks1 x is well to h "s sort ( concrete picture ( molecul> /ructure4 ,x is possible to repres5t ! tetraval5t c>bon atom 9 ! =m ( a tetrah$ron1 & to consid] ! unit$ atoms or atomic gr\ps z plac$ at ! f\r v]tices4 ,) su* a spatial repres5tation we c get an idea ab\t _m *emical que/ions :i* o!rwise w\ld be difficult to expla94 ,we "k1 = example1 t two comp\nd molecules hav+ ! same k9d & numb] ( atoms & ! same bonds 7& h5ce ! same /ructural =mul71 may yet be diff]5t 9 t !y are images ( ea* o!r l a pair ( gloves4 ,sub/ances ^: molecules are symmetrical 9 ?is way c be di/+ui%$ f ea* o!r by _! diff]5t action on ! passage ( light4 ,?is molecul> *emi/ry ( space1 or /]eo-*emi/ry z x is call$1 has prov$ ( great importance 9 expla9+ difficult problems 9 organic *emi/ry1 i4e4 ! *emi/ry ( c>bon4 ,al?\gh !re h nev] be5 _m *emi/s :o really h believ$ ! c>bon atom to be a rigid tetrah$ron1 we mu/ admit t 9 ?is way x has be5 possible to get on ! track ( ! secrets ( atomic /ructure4 ,9 comp>+ ! prop]ties ( ! elem5ts ) _! atomic weights1 !re has be5 discov]$ a peculi> relation :i* rema9$ = a long "t )\t explanation1 b :i* lat] sugge/$ a c]ta9 connection betwe5 ! inn] /ructure ( an atom & its *emical prop]ties4 ,we ref] to ! natural or p]iodic sy/em ( ! elem5ts :i* 0 enunciat$ 9 #ahfi by ! ,russian *emi/1 ,m5delejeff1 & ab\t ! same "t & indep5d5tly by ! ,g]man1 ,lo?> ,mey]4 ,?is sy/em w be und]/ood mo/ cle>ly by exam9+ ! table on p4 #bc1 :]e ! elem5ts ) _! respective atomic weights & *emical symbols are arrang$ 9 numb]$ columns s t ! atomic weights increase ^u read+ ! table f left to "r or f top to bottom4 ,x w be se5 t 9 ea* ( ! n9e columns !re are collect$ elem5ts ) relat$ prop]ties1 =m+ :at may be call$ *emical families4 ,! table z "h giv5 is ( a rec5t date & diff]s f ! old table ( ,m5delejeff1 bo? 9 ! great] numb] ( elem5ts & 9 ! p>ticul>s ( ! arrangem5t4 ,) ea* elem5t !re is associat$ a numb] :i* indicates its position 9 ! s]ies ) respect to increas+ atomic weight4 ,?us hydrog5 has ! numb] #a1 helium #b1 etc41 up to uranium1 ! atom ( :i* is ! heavie/ ( any kn[n elem5t1 & to :i* ! numb] #ib is giv54 ,9 ea* ( ! columns ! elem5ts fall naturally into two sub-gr\ps1 & ?is division is indicat$ 9 ! table by plac+ ! *emical symbols to ! "r or left 9 ! column4 ,on close exam9ation x becomes evid5t t ! regul>ity 9 ! sy/em is n entirely simple4 ,fir/ ( all "s cases w be f\nd :]e ! atomic weight ( "o elem5t is great] ?an t ( ! foll[+ elem5t4 7,! cases ( argon & potassium on ! "o h& & cobalt & nickel on ! o!r are examples47 ,su* an int]*ange is absolutely necess>y if ! elem5ts :i* belong to ! same *emical family are to be plac$ 9 ! same column4 ,z a second in/ance ( irregul>ity1 att5tion mu/ be call$ to ,column ,,viii4 9 ! table4 ,:ile 9 ! fir/ score or s ( elem5ts x is always f\nd t two successive elem5ts h diff]5t prop]ties & cle>ly belong to di/9ct *emical families1 9 ! s-call$ iron gr\p 7iron1 cobalt & nickel7 we meet ) a case :]e successive elem5ts resemble ea* o!r 9 _m respects 7= in/ance1 9 _! magnetic prop]ties74 ,s9ce !re are two m su* 8triads0 9 ! p]iodic sy/em1 h[ev]1 we _c prop]ly call ?is an irregul>ity4 ,b 9 addition to ^! difficulties !re is :at we may ev5 call a k9d ( inelegance pres5t$ by ! s-call$ 8r>e e>?s0 gr\p4 ,9 ?is gr\p !re foll[ aft] lan?anum ?irte5 elem5ts ^: prop]ties are r simil>1 s t x is v difficult to sep>ate !m f ea* o!r 9 ! mixtures 9 :i* !y occur 9 ! m9]als ( nature4 7,9 ! table ^! elem5ts are enclos$ 9 a frame47 ,on ! o!r h&1 ! app>5t abs5ce ( an elem5t 9 c]ta9 places 9 ! table 7indicat$ by a da%7 _c by any means be look$ ^u z irregul>4 ,9 ,m5delejeff's fir/ sy/em !re 7 _m vacant spaces4 ,) ! help ( 8 table ,m5delejeff 01 to "s ext5t1 able to pr$ict ! prop]ties ( ! miss+ elem5ts4 ,an example ( ?is is ! case ( ! elem5t betwe5 gallium & ars5ic4 ,?is is call$ g]manium1 & 0 discov]$ to h precisely ! prop]ties :i* _h be5 pr$ict$ = x--a discov]y :i* 0 "o ( ! greate/ triumphs 9 fav\r ( ! reality ( ! p]iodic sy/em4 ,on ! :ole1 ! elem5ts discov]$ s9ce ! "t ( ,m5delejeff h f\nd _! natural positions 9 ! table4 ,?is is se51 = example1 9 ! case ( ! s-call$ 8inactive gases0 ( ! atmosph]e1 helium1 argon1 neon1 x5on1 krypton & niton1 :i* h ! common prop]ty ( be+ able to =m no *emical comb9ations :atev]4 ,_! val5ce is !re=e z]o1 & 9 ! table !y are plac$ by !mselves 9 a sep>ate column head$ ) z]o4 ,to expla9 ! my/]y ( ! p]iodic sy/em1 x 0 necess>y to make cle> n only ! regul>ity ( x1 b also ! app>5t irregul>ities :i* seem$ to be arbitr>y individual peculi>ities ( c]ta9 elem5ts or gr\ps4 ,9 ! p]iodic sy/em1 *emi/ry laid d[n "s r se>*+ te/s = future !ories ( atomic /ructure4 ,,! ,,p]iodic ,,or ,,natural ,,sy/em ,,( ,,! ,,elem5ts ---------------------------------------- ---------------------------------------- ---------------------------------------- -------- #j ,i4 ,,ii4 ,,iii4 ,,iv4 ,v4 ,,vi4 ,,vii4 ,,viii4 #a ,hydrog5 ,h #ajjh ---------------------------------------- ---------------------------------------- ---------------------------------------- -------- #b ,helium #c ,li?ium #d ,b]yllium #e ,boron #f ,c>bon #g ,nitrog5 #h ,oxyg5 #i ,fluor9e ,he #djj ,li #fid ,be #ia ,b #aaj ,c #abj ,n #adj ,o #af ,f #aij ---------------------------------------- ---------------------------------------- ---------------------------------------- ------- #aj ,neon #aa ,sodium #ab ,magnesium #ac ,alum9ium #ad ,silicon #e ,phosphorus #af ,sulphur #ag ,*lor9e ,ne #bjb ,na #bcj ,mg #bdc ,al #bga ,si #bhc ,p #caj ,s #cba ,cl #cee ---------------------------------------- ---------------------------------------- ---------------------------------------- ------- #ah ,argon #ai ,potassium #bj ,calcium #ba ,sc&ium #bb ,titanium #bc ,vanadium #bd ,*romium #be ,manganese #bf ,iron #bg ,cobalt ,a #cii ,k #cia ,ca #dja ,sc #dda ,ti #dha ,v #eaj ,cr #ebj ,mn #edi ,fe #eeh ,co #eij #bh ,nickel ,ni #eh4g ---------------------------------------- ---------------------------------------- ---------------------------------------- ------- #bi ,copp] #cj ,z9c #ca ,gallium #cb ,g]manium #cc ,ars5ic #cd ,sel5ium #ce ,brom9e ,cu #fcf ,zn #fed ,ga #fii ,ge #gbe ,z #gej ,se #gib ,br #gii ---------------------------------------- ---------------------------------------- ---------------------------------------- ------- #cf ,krypton#cg ,rubidium #ch ,/rontium #ci ,yttrium #dj ,zirconium #da ,niobium #db ,molybd5um #dc -- #dd ,ru!nium #de ,rhodium ,kr #hbi ,rb #hed ,sr #hgf ,y #hhg ,zr #ijf ,nb #ice ,mo #ifj ,ru #ajag ,rh #ajbi #df ,palladium ,pd #ajfg ---------------------------------------- ---------------------------------------- ---------------------------------------- ------- #dg ,silv] #dh ,cadmium #di ,indium #ej ,t9 #ea ,antimony #eb ,tellurium #ec ,jod9e ,ag #ajgi ,cd #aabd ,9 #aadh ,sn #aahg ,sb #abjb ,te #abge ,j #abfi ---------------------------------------- -------- #ed ,x5on #ee ,caesium #ef ,b>ium #eg ,lan?anum #eh ,c]ium #ei ,praseodymium #fj ,neodymium #fa -- #fb ,sam>ium ,x #acjb ,cs #acbh ,ba #acgc ,la #acij ,ce #adjb ,pr #adjf ,nd #addc ,sm #aejd #fc ,europium #fd ,gadol9ium #fe ,t]bium #ff ,dysprosium ,eu #aebj ,gd #aegc ,tb #aeib ,dy #afbe #fg ,holmium #fh ,erbium #fi ,?ulium #gj ,ytt]bium #ga ,cassiopeium ,ho #afce ,er #afgg ,tm #afhe ,yb #agcj ,cp #agej ---------------------------------------- -------- #gb ,hafnium #gc ,tantalum #gd ,tung/5 #ge -- #gf ,osmium #gg ,iridium ,hf #agi ,ta #ahae ,w #ahdj ,os #aiji ,ir #aiba #gh ,plat9um ,pt #aieb ---------------------------------------- ---------------------------------------- ---------------------------------------- ------- #gi ,gold #hj ,m]cury #ha ,?allium #hb ,lead #hc ,bismu? #hd ,polonium #he -- ,au #aigb ,hg #bjjf ,tl #bjdj ,pb #bjgb ,bi #bjij ,po #bajj ---------------------------------------- ---------------------------------------- ---------------------------------------- ------- #hf ,niton #hg -- #hh ,radium #hi ,act9ium #ij ,?orium#ia ,protact9ium #ib ,uranium ,ni #bbbj ,ra #bbfj ,ac8 ,? #bcba ,pa8 ,u #bch ---------------------------------------- ---------------------------------------- ---------------------------------------- ------- ,! ,molecul> ,!ory ( ,physics4 ,f a consid]ation ( ! *emical prop]ties ( ! elem5ts we %all n[ turn to an exam9ation ( ! physical *>act]i/ics1 al?\gh 9 a c]ta9 s5se *emi/ry itself is b "o special phase ( physics4 ,if matt] is really con/ruct$ ( indep5d5tly exi/+ p>ticles--atoms & molecules--! int]play ( ! individual p>ts mu/ det]m9e n only ! *emical activities1 b also ! o!r prop]ties ( matt]4 ,s9ce mo/ ( ^! prop]ties are diff]5t = diff]5t sub/ances1 or 9 o!r words are 8molecul> prop]ties10 x is reasonable to suppose t 9 _m cases explanations c be m readily giv5 by consid]+ ! molecules z ! fundam5tal p>ts4 ,x is natural t ! fir/ attempts to develop a molecul> !ory conc]n$ gases1 = _! physical prop]ties are mu* simpl] ?an ^? ( liquids or solids4 ,?is simplicity is inde$ easily und]/ood on ! molecul> !ory4 ,:5 a liquid by evaporation is trans=m$ into a gas1 ! same weight ( ! elem5t has a volume sev]al hundr$ times great] ?an be=e4 ,! molecules1 pack$ toge!r tightly 9 ! liquid1 9 ! gas are sep>at$ f ea* o!r & c move freely )\t influ5c+ ea* o!r appreciably4 ,:5 two ( !m come v close to ea* o!r1 mutually repulsive =ces w arise to prev5t collision4 ,s9ce x mu/ be assum$ t 9 su* a 8collision0 ! individual molecules d n *ange1 !y c !n to a c]ta9 ext5t be consid]$ z ela/ic bodies1 sph]es = in/ance4 ,f consid]ations ( ?is nature ! k9etic !ory ( gases develop$4 ,accord+ to ?is a mass ( gas consi/s ( an imm5se numb] ( v small molecules4 ,ea* molecule travels ) great velocity 9 a /raight l9e until x meets an ob/ruction1 su* z ano!r molecule or ! wall ( ! conta9+ vessel2 aft] su* an enc\nt] ! molecule travels 9 a second direction until x collides aga91 & s on4 ,! pressure ( ! gas on ! wall ( ! conta9] is ! result ( ! v _m collisions :i* ea* little piece ( wall receives 9 a %ort int]val ( "t4 ,! magnitude ( ! pressure dep5ds ^u ! numb]1 mass & velocity ( ! molecules4 ,! velocity w be diff]5t = ! individual molecules 9 a gas1 ev5 if all ! molecules are ( ! same k9d1 b at a giv5 temp]ature an av]age velocity c be det]m9$ & us$4 ,if ! temp]ature is increas$1 ?is av]age molecul> velocity w be increas$1 & if at ! same "t ! volume is kept con/ant1 ! pressure ( ! gas on ! walls w be increas$4 ,if ! temp]ature & ! av]age velocity rema9 con/ant :ile ! volume is halv$1 !re w be twice z _m molecules p] cubic c5timetre z be=e4 ,!re=e1 on ea* squ>e c5timetre ( ! conta9+ wall !re w be twice z _m collisions1 & consequ5tly ! pressure w be d\bl$4 ,boyle's ,law1 t ! pressure ( a gas at a giv5 temp]ature is inv]sely proportional to its volume1 is ?us an imm$iate result ( ! molecul> !ory4 ,! molecul> !ory also ?r[s new light ^u ! correspond5ce betwe5 heat & me*anical "w & ^u ! law ( ! cons]vation ( en]gy1 :i* ab\t ! middle ( ! n9ete5? c5tury 0 enunciat$ by ! ,engli%man1 ,j\le1 ! ,g]mans1 ,may] & ,helmholtz1 & ! ,dane1 ,cold+4 ,a brief discussion ( heat & en]gy w be giv5 "h1 s9ce "s conception ( ^! ph5om5a is necess>y 9 und]/&+ :at foll[s4 ,to lift a /one ( #e p\nds ?r\gh a di/ance ( #aj feet dem&s an exp5diture ( "w am\nt+ to #e #aj #ej foot-p\nds2 b ! /one is n[ enabl$ to p]=m an equally l>ge am\nt ( "w 9 fall+ back ^! #aj feet4 ,! /one1 by its height above ! e>? & by ! attraction ( ! e>?1 n[ has 9 its elevat$ position :at is call$ 8pot5tial0 en]gy to ! am\nt ( #ej foot-p\nds4 ,if ! /one z x falls lifts ano!r weight by "s su* device z a block & tackle1 ! pot5tial en]gy lo/ by ! fall+ /one w be transf]r$ to ! lift$ "o4 ,if ! app>atus is frictionless1 ! fall+ /one c lift #e p\nds #aj feet or #aj p\nds #e feet1 etc41 s t all ! #ej foot-p\nds ( pot5tial en]gy w be /or$ 9 ! second /one4 ,if in/ead ( be+ us$ to lift ! second /one1 ! orig9al /one is all[$ to fall freely or to roll d[n an incl9$ plane )\t friction1 ! velocity w increase z ! /one falls1 &1 z ! pot5tial en]gy is lo/1 ano!r =m ( en]gy1 kn[n z en]gy ( motion or k9etic en]gy1 is ga9$4 ,conv]sely1 a body :5 x loses its velocity c d "w1 su* z /ret*+ a spr+ or sett+ ano!r body 9 motion4 ,let u suppose t ! /one is fa/5$ to a cord & is sw++ l a p5dulum 9 a vacuum :]e !re is no resi/ance to its motion4 ,! p5dulum w alt]nately s9k & rise aga9 to ! same height4 ,z ! p5dulum s9ks1 ! pot5tial en]gy w be *ang$ into k9etic en]gy1 b z x rises aga9 ! k9etic w be ex*ang$ = pot5tial4 ,?us !re is no loss ( en]gy1 b m]ely a cont9u\s ex*ange betwe5 ! two =ms4 ,if a mov+ body meets resi/ance1 or if its free fall is halt$ by a fix$ body1 x might seem z if1 at la/1 ! en]gy 7 lo/4 ,?is1 h[ev]1 is n ! case1 = ano!r trans=mation occurs4 ,e "o kn[s t heat is develop$ by friction1 & t heat c produce "w1 z 9 a /eam-eng9e4 ,c>eful inve/igations h %[n t a giv5 am\nt ( me*anical "w w always produce a c]ta9 def9ite am\nt ( heat1 t is1 #djj foot-p\nds ( "w1 if conv]t$ into heat1 w always produce #a ,b4,t4,u4 ( heat1 :i* is ! am\nt necess>y to raise ! temp]ature ( #a p\nd ( wat] #a ,f4 ,conv]sely1 :5 heat is conv]t$ into "w1 #a ,b4,t4,u4 ( heat 8vani%es0 e "t #djj foot-p\nds ( "w are produc$4 ,heat !n is j a special =m ( en]gy1 & ! developm5t ( heat by friction or collision is m]ely a trans=mation ( en]gy f "o =m to ano!r4 ,) ! assi/ance ( ! molecul> !ory x becomes possible to int]pret z purely me*anical ! trans=mation ( me*anical "w into heat en]gy4 ,let u suppose t a fall+ body /rikes a pi/on at ! top ( a gas-fill$ cyl9d]1 clos$ at ! bottom4 ,if ! pi/on is driv5 d[n1 ! gas w be compress$ & !re=e heat$1 = ! spe$ ( ! molecules w be increas$ by collisions ) ! pi/on 9 its d[nw>d motion4 ,9 ?is example ! k9etic en]gy giv5 to ! pi/on by ! ext]ior fall+ body is us$ to increase ! k9etic en]gy ( ! molecules ( ! gas4 ,:5 ! molecules conta9 m ?an "o atom1 att5tion mu/ also be giv5 to ! rotations ( ! atoms 9 a molecule ab\t ea* o!r4 ,a "p ( any add$ k9etic en]gy 9 ! gas w be us$ to increase ! en]gy ( ! atomic rotations4 ,! next /ep is to assume t1 9 solids & liquids1 heat is purely a molecul> motion4 ,"h1 too1 ! developm5t ( heat aft] collision ) a mov+ body %\ld be treat$ z a trans=mation ( ! k9etic en]gy ( an individual1 visible body into an inn] k9etic en]gy1 divid$ among ! innum]able invisible molecules ( ! heat$ solid or liquid4 ,9 consid]+ ! int]nal conduct ( gases x is unnecess>y 7at lea/ 9 ! ma97 to consid] any inn] =ces except ! repulsions 9 ! collisions ( ! molecules4 ,9 solids & liquids1 h[ev]1 ! attractions ( ! tightly pack$ molecules = ea* o!r mu/ n be neglect$4 ,inde$ ! situation is too complicat$ to be expla9$ by any simple molecul> !ory4 ,n all en]gy trans=mations c be consid]$ z purely me*anical4 ,= in/ance1 heat c be produc$ 9 a body by rays f ! sun or f a hot fire1 &1 conv]sely1 a hot body c lose its heat by radiation4 ,"h1 also1 we are conc]n$ ) trans=mations ( en]gy2 !re=e ! law = ! cons]vation ( en]gy /ill holds1 i4e4 ! total am\nt ( en]gy c nei!r be increas$ nor decreas$ by trans=mations f "o =m to ano!r4 ,= ! production ( #a ,b4,t4,u4 ( heat a def9ite am\nt ( radiation en]gy is requir$2 conv]sely1 ! same am\nt ( radiation en]gy is produc$ :5 #a ,b4,t4,u4 ( heat is trans=m$ into radiation4 ,?is *ange _c1 h[ev]1 be expla9$ z ! result ( me*anical int]play betwe5 bodies 9 motion4 ,! me*anical !ory ( heat is v useful :5 we re/rict ourselves to ! transf] ( heat f "o body to ano!r1 :i* is 9 contact ) x4 ,:5 appli$ to gases ! !ory leads directly to ,avogadro's ,law4 ,if two masses ( gas h ! same temp]ature1 i4e41 if no ex*ange ( heat betwe5 !m takes place ev5 if !y are 9 contact ) ea* o!r1 !n ! av]age value ( ! k9etic en]gy ( ! molecules mu/ be ! same 9 bo? gases4 ,if "o gas is hydrog5 & ! o!r oxyg51 ! light] hydrog5 molecules mu/ h a great] velocity ?an ! heavi] oxyg5 molecules2 o!rwise !y _c h ! same k9etic en]gy 7! k9etic en]gy ( a body is "o-half ! product ( ! mass & ! squ>e ( ! velocity74 ,s9ce ! pressure ( a gas dep5ds ^u ! k9etic en]gy ( ! molecules & ^u _! numb] p] cubic c5timetre1 at ! same temp]ature & pressure equal volumes mu/ conta9 equal numb]s ( oxyg5 & ( hydrog5 molecules4 ,z ,j\le %[$ 9 #ahea1 f ! mass ( a gas p] cubic c5timetre & f its pressure p] squ>e c5timetre1 ! av]age velocity ( ! molecules c be calculat$4 ,= hydrog5 at #j ,c4 & atmosph]ic pressure ! av]age velocity is ab\t #eejj feet p] second2 = oxyg5 "u ! same conditions x is some?+ ov] #acjj feet p] second4 ,all ^! results ( ! atomic & molecul> !ory1 h[ev]1 gave no in=mation ab\t ! absolute weight ( ! individual atoms & molecules1 nor ab\t _! magnitude nor ! numb] ( molecules 9 a cubic c5timetre at a giv5 temp]ature & pressure4 ,z long z su* que/ions 7 unsolv$ !re 0 a sugge/ion ( unreality 9 ! !ory4 ,! suspicion 0 easily ar\s$ t ! !ory 0 m]ely a conv5i5t s*eme = pictur+ a s]ies ( obs]vations1 & t atoms & molecules 7 m]ely creations ( ! imag9ation4 ,! !ory w\ld seem m plausible if its support]s c\ld say h[ l>ge & h[ heavy ! atoms & molecules 74 ,! molecul> !ory ( gases %[$ h[ to solve ^! problems :i* *emi/ry _h be5 p[]less to solve4 ,let u assume t ! temp]ature ( a mass ( gas is #ajj ,c4 at a c]ta9 altitude1 & #j ,c4 "o metre l[]1 i4e41 ! molecules h diff]5t av]age velocities 9 ! two places4 ,! diff]5ce betwe5 ! velocities w gradually decrease & disappe> on acc\nt ( molecul> collisions4 ,we might expect ?is 8levell+ out0 process or equilibration to proce$ v rapidly because ( ! great velocity ( ! molecules1 b we mu/ consid] ! fact t ! molecules are n entirely free 9 _! movem5ts4 ,9 reality !y w travel b v %ort di/ances be=e meet+ o!r molecules1 & consequ5tly _! directions ( motion w *ange4 ,x is easy to und]/& t ! diff]5ce betwe5 ! velocities ( ! molecules ( ! gas w n disappe> s quickly :5 ! molecules move 9 zigzag l9es ) v %ort /raight /ret*es4 ,! great] velocity 9 "o "p ( ! gas w !n influ5ce ! velocity 9 ! o!r "p only ?r\gh _m int]m$iate /eps4 ,gases are !re=e poor conductors ( heat4 ,:5 ! molecul> velocity ( a gas & its conductivity ( heat are kn[n1 ! av]age l5g? ( ! small /raight pieces ( ! zigzag l9es c be calculat$--9 o!r words1 ! l5g? ( ! mean free pa?4 ,?is l5g? is v %ort2 = oxyg5 at /&>d temp]ature & pressure x is ab\t "o t5-?\s&? ( a millimetre1 or #ja 1 :]e is #jjja millimetre or "o micron4 ,9 addition to ! velocity ( ! molecules1 ! l5g? ( ! mean free pa? dep5ds ^u ! av]age di/ance betwe5 ! c5tres ( two neighb\r+ molecules 79 o!r words1 ^u ! numb] ( molecules p] cubic c5timetre7 & ^u _! size4 ,!re is difficulty 9 def9+ ! size ( molecules because1 z a rule1 ea* conta9s at lea/ two atoms2 b x is helpful to consid] ! molecules1 tempor>ily1 z ela/ic sph]es4 ,ev5 ) ?is assumption we _c yet det]m9e _! dim5sions f ! mean free pa?1 s9ce !re are two unkn[ns1 ! dim5sions ( ! molecules & _! numb] p] cubic c5timetre4 ,^u ^! two quantities dep5ds1 h[ev]1 also ! volume :i* w conta9 ?is numb] ( molecules1 if !y are pack$ closely toge!r4 ,if we assume t we meet su* a pack+ :5 ! sub/ance is cond5s$ 9 liquid =m1 ?is volume c be calculat$ f a k ( ! ratio betwe5 ! volume 9 liquid =m & ! volume ( ! same mass 9 gase\s =m 7at #j ,c4 & atmosph]ic pressure74 ,!n f ?is result & ! l5g? ( ! mean free pa? ! two unkn[ns c be det]m9$4 ,al?\gh ! assumptions are imp]fect1 !y s]ve to give an idea ab\t ! dim5sions ( ! molecules2 ! results f\nd 9 ?is way are ( ! same ord] ( magnitude z ^? d]iv$ lat] by m p]fect me?ods ( an electrical nature4 ,! radius ( a molecule1 consid]$ z a sph]e1 is ( ! ord] ( magnitude #ja 1 :]e means #aj millimetre or #jjja micron4 ,ev5 if a molecule is by no means a rigid sph]e1 ! value giv5 %[s t ! molecule is almo/ unbelievably small1 or1 9 o!r words1 t x c produce appreciable attraction & repulsion 9 only a v small region 9 space4 ,! numb] ( molecules 9 a cubic c5timetre ( gas at #j ,c4 & atmosph]ic pressure has be5 calculat$ ) fair accuracy z approximately #bg #aj4 ,f ?is numb] & f ! weight ( a cubic c5timetre ( a giv5 gas ! weight ( "o molecule c be f\nd4 ,"o hydrog5 molecule weighs ab\t #afe #aj grams1 & "o gram ( hydrog5 conta9s ab\t #f #aj atoms & #c #aj molecules4 ,! weight ( ! atoms ( ! o!r elem5ts c be f\nd by multiply+ ! weight ( ! hydrog5 atom by ! relative atomic weight ( ! elem5t 9 "q--#af = oxyg51 #ad = nitrog51 etc4 ,if ! pressure on ! gas is r$uc$ z mu* z possible 7to ab\t "o t5-million? ( an atmosph]e7 !re w /ill be #c #aj molecules 9 a cubic c5timetre1 & ! av]age di/ance betwe5 molecules w be ab\t "o micron4 ,! mean free pa? betwe5 two collisions w be consid]able1 ab\t two metres1 = in/ance1 9 ! case ( hydrog54 ,! values f\nd = ! numb]1 weight & dim5sions ( molecules are ei!r s v l>ge or s extremely small t _m p1 in/ead ( hav+ m fai? 9 ! atomic & molecul> !ory1 p]haps may be m ?an ev] incl9$ to suppose ! atoms & molecules to be m]e creations ( ! imag9ation4 ,9 fact1 x is only two or ?ree decades ago t "s physici/s & *emi/s--l$ by ! celebrat$ ,g]man sci5ti/1 ,wilhelm ,o/wald--d5i$ ! exi/5ce ( atoms & molecules1 & ev5 w5t s f> z to try to remove ! atomic !ory f sci5ce4 ,:5 ^! sceptics1 9 def5ce ( _! views1 said t ! atoms & molecules 71 & = ev] w\ld be1 completely inaccessible to obs]vation1 x _h to be admitt$ at t "t t !y 7 seem+ly sure ( _! argum5t1 9 ?is "o objection at any rate4 ,a s]ies ( rem>kable discov]ies at ! close ( ! n9ete5? c5tury s increas$ our k ( ! atoms & improv$ ! me?ods ( /udy+ !m t all d\bts ab\t _! exi/5ce _h to be sil5c$4 ,h[ev] incr$ible x may s\nd1 we are n[ 9 a position to exam9e _m ( ! activities ( a s+le atom1 & ev5 to c\nt atoms1 "o by "o1 & to photograph ! pa? ( an individual atom4 ,all ^! discov]ies dep5d ^u ! behavi\r ( atoms z electrically *>g$1 mov+ "u ! influ5ce ( electrical =ces4 ,?is subject w be develop$ 9 ano!r section aft] a discussion ( "s ph5om5a ( light1 an und]/&+ ( :i* is necess>y = ! appreciation ( ! !ory ( atomic /ructure propos$ by ,niels ,bohr4 ,9 ! molecul> !ory ( gases1 :]e we h to d ) neutral molecules1 mu* progress has 9 ! la/ ye>s be5 made by ! ,dane1 ,m>t9 ,knuds51 9 8 exp]im5ts at a v l[ pressure1 :5 ! molecules c travel relatively f> )\t collid+ ) o!r molecules4 ,:ile 8 rese>*es give in=mation on _m int]e/+ & important details1 8 "w gives at ! same "t evid5ce ( a v direct nature conc]n+ ! exi/5ce ( atoms & molecules4 ,,*apt] ,,ii ,,light ,,waves ,,& ,,! ,,spectrum ,! ,wave ,!ory ( ,light4 ,!re h be5 sev]al !ories ab\t ! nature ( light4 ,! great ,engli% physici/1 ,isaac ,newton 7#afdb-agbg71 :o 0 a pione] 9 ! /udy ( light z well z 9 t ( me*anics1 fav\r$ an atomic explanation ( light2 i4e41 he ?\ght t x consi/$ ( p>ticles or light corpuscules :i* 7 emitt$ f lum9\s bodies l projectiles f a cannon4 ,9 contra/ to ?is 8emission0 !ory 0 ! wave !ory ( ,newton's contempor>y1 ! ,dut* sci5ti/1 ,huyg5s4 ,accord+ to him1 light 0 a wave motion pass+ f lum9\s bodies into a sub/ance call$ ! e!r1 :i* fill$ ! o!rwise empty univ]se & p]meat$ all bodies1 at lea/ all transp>5t ones4 ,9 ! n9ete5? c5tury ! wave !ory1 p>ticul>ly ?r\gh ! "w ( ! ,engli%man1 ,"y1 & ! ,fr5*man1 ,fresnel1 came to prevail ov] ! emission !ory4 ,s9ce ! wave !ory plays an important "p 9 ! foll[+ *apt]s1 a discussion ( ! g5]al *>act]i/ics ( all wave motions is appropriate "h4 ,! examples w include wat] waves on ! surface ( a body ( wat]1 & s\nd waves 9 air4 ,illu/ration3 ,,fig4 #d4--,photograph ( ! int]f]5ce betwe5 two simil> wave sy/ems4 ,illu/ration3 ,,fig4 #e4--;,a section ( ! same picture enl>g$4 7,f ,grimsehl1 ,lehrbu* d] ,physik47 ,let u suppose t we are 9 a boat :i* is an*or$ on a body ( wat] & let u wat* ! regul> waves :i* pass u4 ,if !re is nei!r w9d nor curr5t1 a light body l a cork1 ly+ on ! surface1 rises ) ! wave cre/s & s9ks ) ! tr\ghs1 go+ =w>d slightly ) ! =m] & backw>d ) ! latt]1 b rema9+1 on ! :ole1 9 ! same spot4 ,s9ce ! cork foll[s ! surr\nd+ wat] p>ticles1 x %[s _! movem5ts1 & we ?us see t ! individual p>ticles are 9 oscillation1 or m accurately1 9 circulation1 "o circulation be+ complet$ dur+ ! "t 9 :i* ! wave motion advances a wave-l5g?1 i4e41 ! di/ance f "o cre/ to ! next4 ,?is int]val ( "t is call$ ! "t ( oscillation1 or ! p]iod4 ,if ! numb] ( cre/s pass$ 9 a giv5 "t is c\nt$1 ! oscillations ( ! individual p>ticles 9 ! same "t c be det]m9$4 ,! numb] ( oscillations 9 ! unit ( "t1 :i* we "h may take to be "o m9ute1 is call$ ! frequ5cy4 ,if ! frequ5cy is =ty & ! wave-l5g? is ?ree metres1 ! wave progresses #c #dj #abj metres 9 "o m9ute4 ,! velocity ) :i* ! wave motion advances1 or 9 o!r words its velocity ( propagation1 is !n #abj metres p] m9ute4 ,we ?us h ! rule t velocity ( propagation is equal to ! product ( frequ5cy & wave-l5g? 7cf4 ,fig4 #h74 ,on ! surface ( a body ( wat] !re may exi/ at ! same "t sev]al wave sy/ems2 l>ge waves creat$ by w9ds :i* h !mselves p]haps di$ d[n1 small ripples produc$ by breezes & runn+ ov] ! l>g] waves1 & waves f %ips1 etc4 ,! =m ( ! surface & ! *anges ( =m may ?us be v complicat$2 b ! problem is simplifi$ by comb9+ ! motions ( ! individual wave sy/ems at any giv5 po9t4 ,if "o sy/em at a giv5 "t gives a cre/ & ano!r at ! same in/ant also gives a cre/ at ! same po9t1 ! two toge!r produce a high] cre/4 ,simil>ly1 ! resultant ( two simultane\s tr\ghs is a deep] tr\gh2 a cre/ f "o sy/em & a simultane\s tr\gh f ! o!r p>tially de/roy or neutralize ea* o!r4 ,a v int]e/+ yet simple case ( su* 8int]f]5ce0 ( two wave sy/ems is obta9$ :5 ! sy/ems h equal wave-l5g?s & equal amplitudes4 ,su* an int]f]5ce c be produc$ by ?r[+ two /ones1 z mu* alike z possible1 into ! wat] at ! same "t1 at a %ort di/ance f ea* o!r4 ,:5 ! two sets ( wave r+s meet !re is creat$ a network ( cre/s & tr\ghs4 ,figs4 #d & #e %[ photographs ( su* an int]f]5ce1 produc$ by sett+ 9 oscillation two sph]es :i* 7 susp5d$ ov] a body ( wat]4 ,illu/ration3 ,,fig4 #f4--,s*ematic repres5tation ( an int]f]5ce4 ,9 ,fig4 #f !re is a s*ematic repres5tation ( an int]f]5ce ( ! same nature4 ,let u exam9e ! situation at po9ts along ! l[] b\nd>y l9e4 ,at #j1 :i* is equidi/ant f ! two wave c5tres1 !re is evid5tly a wave cre/ 9 ea* sy/em2 !re=e !re is a resultant cre/ ( d\ble ! amplitude ( a s+le cre/ if ! two sy/ems h ! same amplitude4 ,half a p]iod lat] !re is a tr\gh 9 ea* sy/em ) a resultant tr\gh ( twice ! amplitude ( a s+le tr\gh4 ,?us high] cre/s & deep] tr\ghs alt]nate4 ,! same situation is f\nd at po9t #b1 a wave-l5g? f>!r f ! left ?an f ! "r wave c5tre2 9 fact1 ^! results are f\nd at all po9ts su* z #b1 #b1 #d & #d1 :]e ! diff]5ce 9 di/ance f ! two wave c5tres is an ev5 numb] ( wave-l5g?s4 ,at ! po9t #a1 on ! o!r h&1 :]e ! diff]5ce betwe5 ! di/ance f ! c5tres is "o-half a wave-l5g?1 a cre/ f "o sy/em meets a tr\gh f ! o!r1 & ! resultant is nei!r cre/ nor tr\gh b z]o4 ,!re is ! same result at po9ts #a1 #c1 #c1 #e1 #e1 etc41 :]e ! diff]5ce betwe5 ! di/ances f ! two wave c5tres is an odd numb] ( half wave-l5g?s4 ,by ?r[+ a /one into ! wat] 9 front ( a smoo? wall an int]f]5ce is obta9$1 simil> to ! "o describ$ above4 ,! waves are reflect$ f ! wall z if !y came f a c5tre at a po9t beh9d ! wall & symmetrically plac$ ) respect to ! po9t :]e ! /one actually falls4 ,illu/ration3 ,,fig4 #g4--,waves :i* are reflect$ by a bo>d & pass ?r\gh a hole 9 x4 ,:5 a wave sy/em meets a wall 9 :i* !re is a small hole1 ?is op5+ acts z a new wave c5tre1 f :i*1 on ! o!r side ( ! wall1 !re spread half-r+s ( cre/s & tr\ghs4 ,b if ! waves are small & ! op5+ is l>ge 9 proportion to ! wave-l5g?1 ! case is ess5tially diff]5t4 ,let u suppose t wave r+s orig9ate at e po9t ( ! op5+4 ,z a result ( ! co-op]ation ( all ^! wave sy/ems ! cre/s & tr\ghs w advance1 j z be=e1 9 ! orig9al direction ( propagation1 i4e41 along /raight l9es drawn f ! orig9al wave c5tre ?r\gh ! op5+2 l9es ( radiation1 we may call !m4 ,x c be %[n1 h[ev]1 t z ^! l9es ( radiation deviate m & m f ! normal to ! wall1 ! int]f]5ce betwe5 wave sy/ems weak5s ! resultant wave motion4 ,if ! deviation f ! normal to ! wall is increas$1 ! weak5+ v>ies 9 magnitude1 provid$ t ! waves are suffici5tly small2 b ev5 if ! wave motions at times may ?us 8fl>e up0 some:at1 /ill on ! :ole !y w decrease z ! deviation f ! normal to ! wall is increas$4 ,! small] ! waves 9 comp>ison to ! op5+1 ! m m>k$ is ! decrease ( ! wave motions z ! di/ance f ! normal to ! wall is increas$1 & ! m ne>ly ! waves w move on 9 /raight l9es4 ,t light moves 9 /raight l9es1 s t opaque objects ca/ %>p %ad[s1 is !re=e consi/5t ) ! wave !ory1 provid$ ! light waves are v small2 ?\gh x is reasonable to expect t on ! passage ( light ?r\gh n>r[ op5+s !re w be produc$ an appreciable b5d+ 9 ! direction ( ! rays4 ,?is supposition agrees entirely ) exp]im5t4 ,z e>ly z ! middle ( ! sev5te5? c5tury1 ! ,italian ,grimaldi discov]$ su* a diffraction ( light :i* passes ?r\gh a n>r[ op5+ into a d>k room4 ,illu/ration3 ,,fig4 #h4--,s*ematic repres5tation ( a wave4 ,a & ,b d5ote cre/s2 ,c d5otes a tr\gh4 wave-l5g?4 amplitude ( wave4 ,if ,t d5otes ! "t ! wave takes to travel f ,a to ,b1 & #a_/,t ! frequ5cy1 ! wave velocity v w be equal to _/,t 4 ,po9ts ,p & ,p are po9ts 9 ! same phase4 ,9 bo? light & s\nd ! use ( su* t]ms z wave & wave motion is figurative1 = cre/s & tr\ghs are lack+4 ,b ?is *oice ( t]ms is comm5dable1 because s\nd & light possess an ess5tial prop]ty simil> to "o possess$ by wat] waves4 ,:at happ5s :5 a tun+-=k emits s\nd waves into ! surr\nd+ air1 is t ! air p>ticles are set 9 oscillation 9 ! direction ( ! propagation ( s\nd4 ,all ! p>ticles ( air h ! same p]iod z ! tun+-=k1 & ! numb] ( oscillations p] second det]m9es ! pit* ( ! note produc$2 b ! air p>ticles at diff]5t di/ances f ! tun+-=k are n all simultane\sly 9 ! same phase or condition ( oscillation4 ,if "o p>ticle1 at a c]ta9 di/ance f ! s\rce ( s\nd & at a giv5 "t1 is mov+ mo/ rapidly away f ! s\rce1 !n at ! same "t !re is ano!r p>ticle1 some:at f>!r along ! direction ( propagation1 :i* is mov+ t[>ds ! s\rce mo/ rapidly4 ,?is alt]nation ( direction w exi/ all along ! pa? ( ! s\nd4 ,:]e ! p>ticles are approa*+ ea* o!r1 ! air is 9 a /ate ( cond5sation1 & :]e ! p>ticles are draw+ ap>t1 ! air is 9 a /ate ( r>efaction4 ,:ile ! individual p>ticles are oscillat+ 9 approximately ! same place1 ! cond5sations & r>efactions1 l tr\ghs & cre/s 9 wat]1 advance ) a velocity :i* is call$ ! velocity ( s\nd4 ,if we call ! di/ance betwe5 two consecutive po9ts 9 ! same phase a wave-l5g?1 & ! numb] ( oscillations 9 a p]iod ( "t ! frequ5cy1 !n1 z 9 ! case ( wat] waves1 ! velocity ( propagation w be equal to ! product ( frequ5cy & wave-l5g?4 ,light1 l s\nd1 is a p]iodic *ange ( ! conditions 9 ! diff]5t po9ts ( space4 ,^! *anges :i* emanate f ! s\rce ( light1 9 ! c\rse ( "o p]iod advance "o wave-l5g?1 i4e41 ! di/ance betwe5 two successive po9ts 9 ! same phase & ly+ 9 ! direction ( propagation4 ,z 9 ! cases ( s\nd & wat] waves1 ! velocity ( propagation or ! velocity ( light is equal to ! product ( frequ5cy & wave-l5g?4 ,if ?is velocity is indicat$ by ! lett] c1 ! frequ5cy by & ! wave-l5g? by 1 !n c c c or ---- or ---- 4 ,! velocity ( light 9 free space is a con/ant1 ! same = all wave-l5g?s4 ,x 0 fir/ det]m9$ by ! ,dani% a/ronom] ,ole ,rm] 7#afgf7 by obs]vations ( ! moons ( ,jupit]4 ,accord+ to ! measurem5ts ( ! pres5t day ! velocity ( light is ab\t #a1jjj1jjj1jjj feet or #cjj1jjj kilometres p] second4 ,9 c5timetres x is ?us ab\t #c #aj4 ,ef=ts h be5 made to consid] light waves1 l s\nd waves1 z produc$ by ! oscillations ( p>ticles1 n ( ! air1 b ( a p>ticul> sub/ance1 ! 8e!r10 fill+ & p]meat+ ev]y?+2 b all attempts to =m def9ite repres5tations ( ! mat]ial prop]ties ( ! e!r & ( ! movem5ts ( its p>ticles h be5 unsuccessful4 ,! electromagnetic !ory ( light1 enunciat$ ab\t fifty ye>s ago by ! ,scotti% physici/1 ,maxwell1 has furni%$ in=mation ( an ess5tially diff]5t "* conc]n+ ! nature ( light waves4 ,let u suppose t electricity is oscillat+ 9 a conductor connect+ two metal sph]es1 = in/ance4 ,! sph]es1 !re=e1 h1 alt]nately1 positive & negative *>ges4 ,!n accord+ to ,maxwell's !ory we %all expect t 9 ! surr\nd+ space !re w spread a k9d ( electromagnetic wave ) a velocity equal to t ( light4 ,:]ev] ^! waves are1 !re %\ld arise electric & magnetic =ces at "r angles to ea* o!r & to ! direction ( propagation ( ! waves2 ! =ces %\ld *ange direction 9 rhy?m ) ! movem5ts ( electricity 9 ! emitt+ conductor4 ,by way ( illu/ration let u assume t we h some:]e 9 space an imm5sely small & light body or p>ticle ) an electric *>ge4 ,if1 9 ! region 9 "q1 an electromagnetic wave motion takes place1 !n ! *>g$ p>ticle w oscillate z a result ( ! p]iodically *ang+ electrical =ces4 ,! p>ticle "h plays ! same rle z ! cork on ! surface ( ! wat] 7cf4 p4 #ce72 ! *>g$ body ?us makes ! electrical oscillations 9 space app>5t j z ! cork %[s ! oscillations ( ! wat]4 ,9 addition to ! electrical =ces !re are also magnetic =ces 9 an electromagnetic wave4 ,we c imag9e t !y are made app>5t by us+ a v small /eel magnet in/ead ( ! *>g$ body4 ,accord+ to ,maxwell's !ory1 ! magnet expos$ to ! electromagnetic wave w p]=m rapid oscillations4 ,maxwell came to ! conclusion t light consi/$ ( electromagnetic waves ( a simil> nature1 b mu* m delicate ?an c\ld possibly be produc$ & made visible directly by electrical means4 ,9 ! latt] "p ( ! n9ete5? c5tury ! ,g]man physici/1 ,h4 ,h]tz1 succe$$ 9 produc+ electromagnetic waves ) oscillations ( ! ord] ( magnitude ( #ajj1jjj1jjj p] second1 correspond+ to wave-l5g?s ( ! ord] ( magnitude ( sev]al metres4 c #c #aj 7 ---- -------- #cjj cm474 #aj ,moreov]1 he prov$ ! exi/5ce ( ! oscillat+ electric =ces by produc+ electric sp>ks 9 a circle ( wire held 9 ! pa? ( ! waves4 ,he %[$ also t ^! electromagnetic waves 7 reflect$ & int]f]$ ) ea* o!r accord+ to ! same laws z 9 ! case ( light waves4 ,aft] ^! discov]ies !re c\ld be no reasonable d\bt t light waves 7 actually electromagnetic waves1 b s small t x w\ld be totally impossible to exam9e ! oscillations directly ) ! assi/ance ( electric in/rum5ts4 ,b !re 0 9 ?is "w ( ,h]tz no solution ( ! problems ab\t ! nature ( e!r & ! processes und]ly+ ! oscillations4 ,m & m1 sci5ti/s h be5 incl9$ to re/ satisfi$ ) ! electromagnetic description ( light waves & to give up speculation on ! nature ( ! e!r4 ,inde$1 )9 ! la/ few ye>s1 specially ?r\gh ! influ5ce ( ,e9/e9's !ory ( relativity1 _m d\bts h aris5 z to ! actual exi/5ce ( ! e!r4 ,! disagreem5t ab\t its exi/5ce is1 h[ev]1 m a matt] ( def9ition ?an ( reality4 ,we c /ill talk ab\t light z consi/+ ( e!r waves if we ab&on ! old conception ( ! e!r z a rigid ela/ic body ) def9ite mat]ial prop]ties1 su* z specific gravity1 h>dness & ela/icity4 ,! ,disp]sion ( ,light4 ,x has be5 said t ! wave-l5g? ( light is mu* %ort] ?an t ( ! ,h]tzian waves4 ,?is does n mean t all light waves h ! same wave-l5g? & frequ5cy4 ,! light :i* comes to u f ! sun is compos$ ( waves ( _m diff]5t wave-l5g?s & frequ5cies1 to ea* ( :i* corresponds a p>ticul> col\r4 ,9 ?is respect also light may be comp>$ ) s\nd4 ,9 :atev] way a s\nd is produc$1 x is 9 g5]al ( a complicat$ nature1 compos$ ( _m di/9ct notes1 ea* ) its *>act]i/ic wave-l5g? & frequ5cy4 ,naturally ! air p>ticles _c oscillate 9 sev]al diff]5t ways simultane\sly4 ,at a giv5 "t1 h[ev]1 we c ?9k ( ! cond5sation & r>efactions ( ! air or ! oscillations ( ! p>ticles correspond+ to diff]5t tones1 z comp\nd$ ) ea* o!r 9 a way simil> to t 9 :i* ! resultant cre/s & tr\ghs are produc$ on a body ( wat] ) sev]al coexi/5t wave sy/ems4 ,:5 we say t ! complicat$ wave-movem5t emitt$ f "s s\nd-produc+ in/rum5t consi/s ( diff]5t tones1 ?is does n only mean t we may imag9e x purely ma!matically z resolv$ into a s]ies ( simpl] wave sy/ems4 ,! resolution may also take place 9 a m physical way4 ,let u assume t we h a collection ( /r+s ea* ( :i* w produce a note ( p>ticul> pit*4 ,n[1 if s\nd waves meet ?is collection ( /r+s1 ea* /r+ is set 9 oscillation by ! "o wave 9 ! comp\nd s\nd wave :i* corresponds to x4 ,ea* /r+ is !n said to act z a resonator = ! note 9 "q4 ,! notes :i* set ! resonator /r+s 9 oscillation s\nd m l\dly 9 ! neighb\rhood ( ! resonators2 b1 z ! wave tra9 cont9ues on its j\rney ! tones tak5 out by ! /r+s w become weak 9 contra/ to ^? notes :i* f\nd no correspond+ /r+s4 ,! resonator is said to absorb ! notes ) :i* x is 9 pit*4 ,light :i* is compos$ ( diff]5t col\rs1 i4e41 ( wave sy/ems ) diff]5t wave-l5g?s1 c also be resolv$ or disp]s$1 b by a me?od diff]5t f t 9 ! case ( s\nd4 ,:5 light passes f "o m$ium to ano!r1 z f air to glass or vice v]sa1 x is refract$1 i4e41 ! direction ( ! light rays is *ang$2 b if ! light is compos$ ( diff]5t col\rs ! refraction is accompani$ by a 8spread+0 ( ! col\rs :i* is call$ disp]sion4 ,if we look ?r\gh a glass prism s t ! light f ! object exam9$ mu/ pass 9 & out ?r\gh two faces ( ! prism :i* make n too great an angle ) ea* o!r1 ! light-produc+ object is n only displac$ by ! refraction1 b has col\r$ edges4 ,newton 0 ! fir/ to expla9 ! relation ( ! production ( ! col\rs to refraction4 ,he made an exp]im5t ) sunlight1 :i* he s5t ?r\gh a n>r[ op5+ into a d>k room4 ,! sunlight 0 !n by a glass prism trans=m$ or disp]s$ into a b& ( col\r1 a spectrum consi/+ ( all ! col\rs ( ! ra9b[1 r$1 yell[1 gre51 blue & violet1 9 ! ord] nam$1 & ) cont9u\s transition /ages betwe5 neighb\r+ col\rs4 ,illu/ration3 ,,fig4 #i4--,prism spectroscope4 ,to ! "r is se5 ! collimator1 to ! left ! telescope1 9 ! =egr\nd a s*eme = illum9at+ ! cross-wire4 7,f an old pr9t47 ,9 ,newton's orig9al exp]im5t ! diff]5t wave-l5g?s 7 b imp]fectly sep>at$4 ,a spectrum ) pure wave-l5g?s c be obta9$ ) a spectroscope 7cf4 ,fig4 #i74 ,! light to be inve/igat$ illum9ates an adju/able v]tical slit 9 "o end ( a long tube1 call$ ! collimator1 ) a l5s 9 ! o!r end4 ,if ! slit is 9 ! focal plane ( ! l5s1 ! light at any po9t 9 ! slit goes 9 p>allel rays aft] meet+ ! l5s4 ,x !n meets a prism1 ) v]tical edges1 plac$ on a little revolv+ plat=m4 ,! rays1 refract$ by ! prism1 g 9 a new direction into a telescope ^: objective l5s gives 9 its focal plane1 = e col\r1 a cle> v]tical image ( ! slit4 ,^! images c be exam9$ ?r\gh ! ocul> ( ! telescope2 b s9ce ! diff]5t col\rs are n refract$ equally1 ea* col\r$ image ( ! slit has its own place4 ,! totality ( ! slit images !n =ms a horizontal spectrum ( ! same height z ! individual images4 ,by revolv+ ! collimator diff]5t p>ts ( ! spectrum c be put 9 ! middle ( ! field ( view4 ,to facilitate measurem5ts 9 ! spectrum !re is 9 ! focal plane ( ! collimator a slid+ cross-wire ) an adju/+ screw or a v]tical /r& ( spid] web4 ,illu/ration3 ,,fig4 #aj4--,! mode ( op]ation ( a grat+4 ,a1 grat+2 ,c1 ,d1 ,e 444 ,h1 slits2 ,m ,m1 incid5t rays4 ,:5 ,d ,d1 ,e ,e 444 are a :ole numb] ( wave-l5g?s1 ! light waves :i* move 9 ! direction indicat$ by ,c ,n & are collect$ by a l5s1 at ! focal po9t w all be 9 ! same phase & !re=e w re9=ce ea* o!r4 ,9 o!r directions ! light action f "o slit is comp5sat$ by t f ano!r4 ,in/ead ( us+ ! refraction ( light 9 a prism to sep>ate ! wave-l5g?s1 we c use ! int]f]5ce :i* arises :5 a bundle ( p>allel light waves passes ?r\gh a rul$ grat+1 consi/+ ( a great _m v f9e p>allel l9es1 equidi/ant f ea* o!r2 su* a grat+ c be made by rul+ l9es ) a diamond po9t on ! metal coat+ ( a silv]$ plate ( glass4 ,f ea* l9e !re are s5t out light waves 9 all directions2 b if we are consid]+ light ( "o def9ite col\r 7a giv5 wave-l5g?1 mono*romatic light71 ! int]f]5ce among ! waves f all ! slits practically de/roys all waves except 9 ! direction ( ! orig9al rays & 9 ! directions mak+ c]ta9 angles ) ! =m]1 dep5d5t ^u ! wave-l5g? & ! di/ance betwe5 two successive l9es 7! grat+ space74 ,mono*romatic light c be obta9$ by us+ z ! s\rce ( light a _s flame1 col\r$ yell[ ) common salt 7sodium *loride74 ,if ! slit 9 a spectroscope is light$ ) a yell[ light f su* a flame1 & if a grat+ normal to ! direction ( ! rays is sub/itut$ = ! prism1 !n 9 ! telescope !re is se5 a yell[ image ( ! slit1 & on ea* side ( x "o1 two1 ?ree or m yell[ images4 ,if sunlight is us$ ! c5tral image is :ite1 s9ce all ! col\rs are "h assembl$4 ,! o!r images become spectra because ! diff]5t col\rs are unequally refract$4 ,9 ^! grat+ spectra1 :i* accord+ to _! di/ance f ! c5tral l9e are call$ spectra ( ! fir/1 second or ?ird ord]1 ! violet "p lies ne>e/ to ! c5tral l9e1 ! r$ "p f>!/ away4 ,s9ce ! deflection is ! great] ! great] ! wave-l5g?1 !n violet light mu/ h ! %orte/ wave-l5g? & r$ ! greate/4 ,f ! am\nt ( ! refraction & ! size ( ! grat+ space ! wave-l5g? ( ! light "u inve/igation c be calculat$4 ,= ! yell[ light f our _s flame ! wave-l5g? is ab\t #jjjjehi mm4 or #jehi or #ehi 4 ,9 c5timetres ! wave-l5g? is #jjjjjehi cm42 f ! =mula c_/1 #ebf #aj4 ,! frequ5cy is ?us almo/ inconceivably l>ge4 ,= ! mo/ di/ant r$ & violet 9 ! spectrum ! wave-l5g?s are respectively ab\t #hjj & #djj 1 & ! frequ5cies #cge #aj & #gej #aj oscillations p] second4 ,9 sci5tific exp]im5ts a grat+ ( specul> metal ) p>allel rul+s is sub/itut$ = ! transp>5t grat+4 ,! spectrum is !n giv5 by ! reflect$ light f ! p>ts betwe5 ! rul+s4 ,specul> grat+s c be made by rul+ on a concave mirror1 :i* focuses ! rays s t a glass l5s is unnecess>y4 ,grat+s ) sev]al hundr$ l9es or rul+s to ! millimetre give excell5t spectra1 ) /r5g? ( light & m>k$ disp]sion4 ,! prep>ation ( ! fir/ really good grat+s is due to ! exp]im5tal skill ( ! ,am]ican1 ,r[l&1 :o 9 #ahgj built a divid+ eng9e f :i* ! great] "p ( ! good grat+s n[ 9 use orig9ate4 ,! contribution :i* ,r[l& !reby made to physical sci5ce c h>dly be ov]-e/imat$4 ,spectral ,l9es4 ,9 ! e>ly "p ( ! n9ete5? c5tury ,wolla/on1 9 ,engl&1 & lat] ,fraunh(] 9 ,g]many1 discov]$ d>k l9es 9 ! sol> spectrum1 a discov]y :i* meant t c]ta9 col\rs 7 miss+4 ,! mo/ noticeable ( ^! s-call$ 8,fraunh(] ,l9es0 7 nam$ ) ! lett]s ,a1 ,b1 ,c1 ,d1 ,e1 ,f1 ,g1 ,h1 f r$ to violet4 ,x 0 lat] discov]$ t "s ( ! l9es 7 d\ble1 t ! ,d-l9e1 = in/ance1 c be resolv$ into ,d & ,d2 o!r lett]s1 su* z b & h1 7 introduc$ to d5ote new l9es4 ,) improvem5ts 9 ! me?ods ( exp]im5t & rese>* ! numb] ( l9es has increas$ to hundr$s & ev5 ?\s&s4 ,! light f a gl[+ solid or liquid elem5t =ms1 on ! o!r h&1 a cont9u\s spectrum1 i4e4 a spectrum :i* has no d>k l9es4 ,an illu/ration ( ! sol> spectrum ) ! /ronge/ ,fraunh(] l9es is giv5 at ! end ( ! book4 ,9 contra/ to ! sol> spectrum ) d>k l9es on a bright backgr\nd are ! s-call$ l9e spectra1 :i* consi/ ( bright l9es on a d>k backgr\nd4 ,! fir/ kn[n l9e spectrum 0 ! "o giv5 by light f ! _s flame col\r$ ) common salt1 m5tion$ 9 connection ) mono*romatic light4 ,z has be5 said1 ?is spectrum _h j "o yell[ l9e :i* 0 lat] f\nd to consi/ ( two l9es close to ea* o!r4 ,x is sodium *loride :i* col\rs ! flame yell[4 ,! col\r is due1 n to ! *lor9e1 b to ! sodium1 = ! same d\ble yell[ l9e c be produc$ by us+ o!r sodium salts n comp\nd$ ) *lor9e4 ,! yell[ light is !re=e call$ sodium light4 ,no4 #g 9 ! table ( spectra at ! end ( ! book %[s ! spectrum produc$ by sodium vap\r 9 a flame4 7,on acc\nt ( ! small scale 9 ! figure x is n %[n t ! yell[ l9e is d\ble47 ,ano!r int]e/+ discov]y 0 soon made1 namely1 t ! sodium l9e has exactly ! same wave-l5g? z ! light lack+ 9 ! sol> spectrum1 :]e ! d\ble ,d-l9e is locat$4 ,ab\t #ahfj ,kir*h(f & ,buns5 expla9$ ?is rem>kable co9cid5ce z well z o!rs ( ! same nature4 ,!y %[$ by direct exp]im5t t if sodium vap\r is at a high temp]ature x c n only s5d out ! yell[ light1 b also absorb light ( ! same wave-l5g? :5 rays f a /ill w>m] gl[+ body pass ?r\gh ! vap\r4 ,?is ph5om5on is some?+ l t 9 ! case ( s\nd waves :]e a resonator absorbs ! pit* :i* x c emit itself4 ,! exi/5ce ( ! d>k ,d-l9e 9 ! sol> spectrum mu/ !n mean t 9 ! out] lay] ( ! sun !re is sodium vap\r pres5t ( l[] temp]ature ?an ! :ite-hot int]ior ( ! sun1 & t ! light correspond+ to ! ,d-l9e is absorb$ by ! vap\r4 ,sev]al +5i\s exp]im5ts1 :i* _c be describ$ "h1 h giv5 fur!r evid5ce 9 fav\r ( ?is explanation4 ,9 ! o!r l9e spectra1 j z 9 t f ! common salt flame1 def9ite l9es correspond to def9ite elem5ts & n to *emical comp\nds4 ,! emission ( ^! l9es is !n n a molecul> *>act]i/ic1 b an atomic "o4 ,! l9e spectra ( metals c (t5 be produc$ by vaporiz+ a metallic salt 9 a _s flame or 9 a hot1 col\rless gas flame 7f a ,buns5 burn]74 ,x is ev5 bett] to use an electric arc or /rong electric sp>ks4 ,! atoms f :i* gase\s molecules are =m$ c also be made to emit light :i* by means ( ! spectroscope is %[n to consi/ ( a l9e spectrum4 ,^! results are obta9$ by means ( electric dis*>ges ( v>i\s k9ds1 arcs1 & sp>k dis*>ges ?r\gh tubes :]e ! gas is 9 a r>efi$ /ate4 ,! o!r ,fraunh(] l9es 9 ! sol> spectrum correspond to bright l9es 9 ! l9e spectra ( c]ta9 elem5ts :i* exi/ "h on e>?4 ,^! ,fraunh(] l9es mu/ !n be assum$ to be caus$ by ! absorption ( light by ! elem5ts 9 "q4 ,?is may be expla9$ by ! pres5ce ( ^! elem5ts z gases 9 ! sol> atmosph]e1 ?r\gh :i* passes ! light f ! inn] lay]4 ,?is inn] surface w\ld 9 itself emit a cont9u\s spectrum4 ,! "w ( ,kir*h(f & ,buns5 put at ! disposal ( sci5ce became a new tool ( incalculable scope4 ,fir/ & =emo/1 spectrum exam9ations 7 tak5 into ! s]vice ( *emi/ry z spectrum analysis4 ,x has ?us become possible to analyse quantities ( matt] s small t ! g5]al me?ods ( *emi/ry w\ld be q p[]less to detect !m4 ,x is also possible by spectrum analysis to detect m9ute traces ( an elem5t2 sev]al elem5ts 7 9 ?is way fir/ discov]$ by ! spectroscope4 ,moreov]1 *emical analysis has be5 ext5d$ to ! /udy ( ! sun & />s4 ,! spectral l9es h giv5 u answ]s to _m problems ( physics--problems :i* =m]ly seem$ insoluble4 ,la/ b n lea/ spectrum analysis has giv5 u a key to ! deepe/ secrets ( ! atom1 a key :i* ,niels ,bohr has taught u h[ to use4 ,9 ! discussion ( ! spectrum we h hi!rto re/rict$ ourselves to ! visible spectrum limit$ on ! "o side by r$ & on ! o!r by violet4 ,b ^! b\nd>ies are 9 reality =tuit\s1 det]m9$ by ! human eye4 ,! spectrum c be /udi$ by o!r me?ods ?an ^? ( direct obs]vation4 ,! m indirect me?ods include ! effect ( ! rays on photographic plates & _! heat+ effect on f9e conduct+ wires = electricity1 held 9 v>i\s p>ts ( ! spectrum4 ,x has ?us be5 discov]$ t beyond ! visible violet end ( ! spectrum !re is an ultra-violet region ) /rong photographic activity & an infra-r$ region produc+ m>k$ heat effects4 ,!re are bo? d>k & light spectral l9es 9 ^! new p>ts ( ! spectrum4 ,! fact t glass is n transp>5t to ultra-violet or infra-r$ rays has be5 an ob/acle 9 ! exp]im5ts1 b ! difficulty c be ov]come by us+ o!r sub/ances1 su* z qu>tz or rock salt1 = ! prisms & l5ses1 or by sub/itut+ concave grat+s4 ,by special means x has be5 possible to detect rays ) wave-l5g?s z great z #cjj & z small z ab\t #jjb 1 correspond+ to frequ5cies betwe5 #aj1 & #ae #aj vibrations p] second1 :ile ! wave-l5g?s ( ! lum9\s rays lie betwe5 #jh & #jd 4 ,! t]m 8light wave0 is (t5 us$ to ref] to ! ultra-violet & infra-r$ rays :i* c be %[n 9 ! spectra produc$ by prisms or grat+s4 ,illu/ration3 ,,fig4 #aa4--,photographic effect ( ,x-rays1 :i* are pass$ ?r\gh ! atom grat+ 9 a magnesia cry/al4 ,! electrically produc$ electromagnetic waves1 z already m5tion$1 h wave-l5g?s mu* great] ?an #cjj 4 ,9 wireless telegraphy !re are g5]ally us$ wave-l5g?s ( "o kilometre or m1 correspond+ to frequ5cies ( #cjj1jjj vibrations p] second or less4 ,by direct electrical me?ods x has1 h[ev]1 n be5 possible to obta9 wave-l5g?s less ?an ab\t "o-half a c5timetre1 a l5g? diff]+ consid]ably f ! #jc millimetre wave ( ! longe/ infra-r$ rays4 ,wave-l5g?s mu* less ?an #jjb or #bj exi/ 9 ! s-call$ ,rntg5 rays or ,x-rays ) wave-l5g?s z small z #jja correspond+ to a frequ5cy ( #cj #aj4 ,^! rays _c possibly be /udi$ ev5 ) ! f9e/ artificially made grat+s1 b cry/als1 on acc\nt ( ! regul> arrangem5t ( ! atoms1 give a k9d ( natural grat+ ( extraord9>y f95ess4 ,) ! use ( cry/al grat+s success has be5 atta9$ 9 decompos+ ! ,rntg5 rays into a k9d ( spectrum1 9 measur+ ! wave-l5g?s ( ! ,x-rays & 9 /udy+ ! int]ior /ructure ( ! cry/als4 ,! ,g]man ,laue1 ! discov]] ( ! peculi> action ( cry/als on ,x-rays 7#aiab71 let ! ,x-rays beams pass ?r\gh ! cry/al1 obta9+ !reby photographs ( ! k9d illu/rat$ 9 ,fig4 #aa4 ,lat] on ess5tial progress 0 due to ! ,engli%m51 ,w4 ,h4 & ,w4 ,l4 ,bragg1 :o work$ out a me?od ( inve/igation by :i* beams ( ,x-rays are reflect$ f cry/al faces4 ,! greate/ wave-l5g? :i* x has be5 possible to measure = ,x-rays is ab\t #ae 1 :i* is /ill a long way f ! #bj ( ! fur!rmo/ ultra-violet rays4 ,x may be said t ! spectrum s9ce ,fraunh(] has be5 made n only long] b also f9]1 = ! accuracy ( measur+ wave-l5g?s has be5 mu* increas$4 ,x is n[ possible to det]m9e ! wave-l5g? ( a l9e 9 ! spectrum to ab\t #jjja or ev5 less1 & to measure extraord9>ily small *anges 9 wave-l5g?s1 caus$ by diff]5t physical influ5ces4 ,9 addition to ! cont9u\s spectra emitt$ by gl[+ solids or liquids1 & to ! l9e spectra emitt$ by gases1 & to ! absorption spectra ) d>k l9es1 !re are spectra ( /ill ano!r k9d4 ,^! are ! absorption spectra :i* are produc$ by ! passage ( :ite light ?r\gh col\r$ glass or col\r$ fluids4 ,"h in/ead ( f9e d>k l9es !re are broad] d>k absorption b&s1 ! spectrum be+ limit$ to ! individual bright p>ts4 ,!re are also ! b& spectra prop]1 :i*1 l ! l9e spectra1 are purely emission spectra1 giv5 by ! light f gases "u p>ticul> conditions2 ^! seem to consi/ ( a s]ies ( bright b&s :i* foll[ ea* o!r ) a c]ta9 regul>ity 7cf4 ,fig4 #ab74 ,) /rong] disp]sion ! b&s are %[n to consi/ ( gr\ps ( bright l9es4 ,illu/ration3 ,,fig4 #ab4--,spectra produc$ by dis*>ges ( diff]5t "* ?r\gh a glass tube conta9+ nitrog5 at a pressure ( _/ t ( ! atmosph]e4 ,above1 a b& spectrum2 bel[1 a l9e spectrum4 ,s9ce ! l9e spectra are mo/ important 9 ! atomic !ory1 we %all exam9e !m "h m c>efully4 ,! l9e spectra ( ! v>i\s elem5ts diff] v mu* f ea* o!r ) respect to _! complexity4 ,:ile _m metals give a great numb] ( l9es 7iron1 = in/ance1 gives m ?an five ?\s&71 o!rs give only a few1 at lea/ 9 a simple spectroscope4 ,) a m p[]ful spectroscope ! simplicity ( /ructure is lo/1 s9ce weak] l9es appe> & o!r l9es :i* _h seem$ s+le are n[ se5 to be d\ble or triple4 ,moreov]1 ! numb] ( l9es is increas$ by ext5d+ ! inve/igation to ! ultra-violet & infra-r$ regions ( ! spectrum4 ,! sodium spectrum1 at fir/1 seem$ to consi/ ( "o s+le yell[ l9e1 b lat] ?is 0 %[n to be a d\ble l9e1 & /ill lat] sev]al pairs ( weak] d\ble l9es 7 discov]$4 ,! k9d & numb] ( l9es obta9$ dep5ds n only ^u ! effici5cy ( ! spectroscope1 b also ^u ! physical conditions "u :i* ! spectrum is obta9$4 ,! eag] attempts ( ! physici/s to f9d laws gov]n+ ! di/ribution ( ! l9es h be5 successful 9 "s spectra4 ,= in/ance1 ! l9e spectra ( li?ium1 sodium1 potassium & o!r metals c be arrang$ into ?ree r[s1 ea* consi/+ ( d\ble l9es4 ,! diff]5ce betwe5 ! frequ5cies ( ! two 8compon5ts0 ( ! d\ble l9es 0 f\nd to be exactly ! same = mo/ ( ! l9es 9 "o ( ^! spectra1 & = ! spectra ( diff]5t elem5ts !re 0 discov]$ a simple relation%ip betwe5 ?is diff]5ce 9 frequ5cy & ! atomic weight ( ! elem5t 9 "q4 ,b ?is regul>ity 0 b a scrap1 s to speak2 sci5ti/s 7 /ill v f> f a law :i* c\ld exactly acc\nt = ! di/ribution ( l9es 9 a s+le s]ies1 n to m5tion ! l9es 9 an entire spectrum or 9 all ! spectra4 ,! fir/ important /ep 9 ?is direction 0 made ab\t #ahhe by ! ,swiss physici/1 ,balm]1 9 8 inve/igations ) ! hydrog5 spectrum1 ! simple/ ( all ! spectra4 ,9 ! visible "p !re are j ?ree l9es1 "o r$1 "o gre5-blue & "o violet1 correspond+ to ! ,fraunh(] l9es ,c1 ,f & h4 ,^! hydrog5 l9es are n[ g5]ally kn[n by ! lett]s ,h1 ,h & ,h4 ,9 ! ultra-violet region !re are _m l9es also4 ,balm] discov]$ t wave-l5g?s ( ! r$ & ( ! gre5 hydrog5 l9e are to ea* o!r exactly z two integ]s1 namely1 z #bg to #bj1 & t ! wave-l5g?s ( ! gre5 & violet l9es are to ea* o!r z #bh to #be4 ,cont9u$ reflection on ?is correspond5ce l$ him to enunciate a rule :i* c be express$ by a simple =mula4 ,:5 frequ5cy is sub/itut$ = wave-l5g? ,balm]'s =mula is writt5 z 7 #a #a 7 ,k7--- - -------71 7 #d n 7 :]e is ! frequ5cy ( a hydrog5 l9e1 ,k a con/ant equal to #cbi #aj & n an integ]4 ,if n takes on diff]5t values1 becomes ! frequ5cy = ! diff]5t hydrog5 l9es4 ,if n #a is negative1 = n #b is z]o4 ,^! values ( n !re=e h no mean+ ) reg>d to 4 ,b if n #c1 !n gives ! frequ5cy = ! r$ hydrog5 l9e ,h2 n #d gives ! frequ5cy ( ! gre5 l9e ,h & n #e t ( ! violet l9e ,h4 ,gradually m ?an ?irty hydrog5 l9es h be5 f\nd1 agree+ accurately ) ! =mula = diff]5t values ( n4 ,"s ( ^! l9es 7 n f\nd 9 exp]im5t1 b 7 discov]$ 9 ! spectrum ( c]ta9 />s2 ! exact agreem5t ( ^! l9es ) ,balm]'s =mula 0 /rong evid5ce = ! belief t !y are due to hydrog54 ,! =mula ?us prov$ itself valuable 9 reveal+ ! secrets ( ! heav5s4 ,z n increases #a_/n approa*es z]o1 & c be made z close to z]o z desir$ by lett+ n increase indef9itely4 ,9 ma!matical t]m9ology1 z n 1 #a_/n #j & ,k_/#d #hbc #aj1 correspond+ to a wave-l5g? ( #cfe 4 ,physically ?is means t ! l9e spectrum ( hydrog5 9 ! ultra-violet is limit$ by a l9e correspond+ to t frequ5cy4 ,ne> ?is limit ! hydrog5 l9es correspond+ to ,balm]'s =mula are tightly pack$ toge!r4 ,= n #bj diff]s b little f ,k_/#d1 & ! di/ance betwe5 two successive l9es correspond+ to an increase ( #a 9 n becomes m & m insignificant4 ,fig4 #ac1 :]e ! numb]s indicate ! wave-l5g?s 9 ! ng/rm unit 7#ja 71 %[s ! cr[d+ ( ! hydrog5 l9es t[>ds a def9ite b\nd>y4 ,! foll[+ table1 :]e ,k has ! accurate value ( #cbijcfd #aj1 %[s h[ exactly ! values calculat$ f ! =mula agree ) exp]im5t4 ,illu/ration3 ,,fig4 #ac4--,l9es 9 ! hydrog5 spectrum correspond+ to ! ,balm] s]ies4 ,,table ,,( ,,"s ,,( ,,! ,,l9es ,,( ,,! ,,balm] ,,s]ies ---------------------------------------- ----------------------- ,k7 - #a_/n7 7calculat$74 7f\nd74 7f\nd74 ---------------------------------------- ---------------------- n #c,k7 - _/ 7 #def1iie bills#def1iif bills#fefdfj ,h n #d,k7 - _/ 7 #faf1idc 8 #faf1idc 8 #dhfbfh 8 ,h n #e,k7 - _/ 7 #fij1igf 8 #fij1igf 8 #dcdafh 8 ,h n #f,k7 - _/ 7 #gca1aib 8 #gca1aic 8 #dajbhh 8 ,h n #g,k7 - _/ 7 #gee1ddj 8 #gee1dda 8 #cigaai 8 ,h ---------------------------------------- ---------------------- n #bj,k7 - _/7 #had1cfe 8 #had1cfa 8 #cfhcjg 8 ---------------------------------------- ---------------------- ,f argum5ts 9 connection ) ! "w ( ! ,sw$i% sci5ti/1 ,rydb]g1 9 ! spectra ( o!r elem5ts1 ,ritz1 a fell[ c\ntryman ( ,balm]'s1 has made x seem probable t ! hydrog5 spectrum conta9s o!r l9es besides ^? correspond+ to ,balm]'s =mula4 ,he assum$ t ! hydrog5 spectrum1 l o!r spectra1 conta9s sev]al s]ies ( l9es & t ,balm]'s =mula corresponds to only "o s]ies4 ,ritz !n enunciat$ a m compreh5sive =mula1 ! ,balm]-,ritz =mula3 7 #a #a 7 ,k7 ------- - -----71 7 n n7 :]e ,k has ! same value z be=e1 & bo? n & n are integ]s :i* c pass ?r\gh a s]ies ( diff]5t values4 ,= n #b1 ! ,balm] s]ies is giv52 to n #a1 & n #b1 #c 444 !re corresponds a second s]ies :i* lies entirely 9 ! ultra-violet region1 & to n #c1 n #d1 #e 444 a s]ies ly+ entirely 9 ! infra-r$4 ,l9es h actually be5 f\nd belong+ to ^! s]ies4 ,=mul1 simil> to ! ,ritz "o1 h be5 set up = ! l9e spectra ( o!r elem5ts1 & repres5t pretty accurately ! di/ribution ( ! l9es4 ,! frequ5cies are ea* repres5t$ by ! diff]5ce betwe5 two t]ms1 ea* ( :i* conta9s an integ]1 :i* c pass ?r\gh a s]ies ( values4 ,b :ile ! hydrog5 =mula1 except = ! ns1 dep5ds only ^u "o con/ant quantity ,k & its t]ms h ! simple =m ,k_/n1 ! =mula is m complicat$ ) ! o!r elem5ts4 ,! t]m c (t5 be writt51 ) a high degree ( exactness1 z ,k_/7n 71 :]e ,k is1 ) consid]able accuracy1 ! same con/ant z 9 ! hydrog5 =mula4 ,= a giv5 elem5t c assume sev]al diff]5t values2 !re=e ! numb] ( s]ies is great] & ! spectrum is ev5 m complicat$ ?an t ( hydrog54 ,all ^! =mul are1 h[ev]1 purely empirical1 d]iv$ f ! values ( wave-l5g?s & frequ5cies f\nd 9 spectrum measurem5ts4 ,!y repres5t c]ta9 m or less simple bookkeep+ rules1 by :i* we c regi/] bo? old & new l9es1 ent] !m 9 r[s1 arrange !m accord+ to a def9ite sy/em4 ,b f ! beg9n+ !re c\ld be no d\bt t ^! rules _h a deep] physical mean+ :i* x 0 n yet possible to "k4 ,!re 0 no visible correspond5ce betwe5 ! spectral l9e =mul & ! o!r physical *>act]i/ics ( ! elem5ts :i* emitt$ ! spectra2 n ev5 9 _! =m did ! =mul %[ any resemblance to =mul obta9$ 9 o!r physical bran*es4 ,,*apt] ,,iii ,,ions ,,& ,,electrons ,e>ly ,!ories & ,laws ( ,electricity4 ,! fundam5tal ph5om5a ( electricity1 :i* 7 fir/ made ! subject ( c>eful /udy ab\t two c5turies ago1 are t c]ta9 sub/ances c be electrifi$ by friction s t someh[ !y c attract light bodies1 & t ! *>ges ( electricity may be ei!r 8positive0 or 8negative40 ,bodies ) l *>ges repel ea* o!r1 :ile ^? ) unlike *>ges attract ea* o!r1 & ei!r p>tially or entirely neutralize ea* o!r :5 !y are br\ght close toge!r4 ,moreov]1 x _h long ago be5 discov]$ t 9 "s sub/ances electricity c move freely f place to place1 :ile 9 o!rs !re is resi/ance to ! movem5t4 ,! =m] bodies are n[ call$ conductors & include metals1 :ile ! latt] are call$ insulators1 glass1 porcela9 & air be+ memb]s ( ?is class4 ,9 ord] to expla9 ! ph5om5a "s imag9$ t !re 7 two k9ds ( 8electric sub/ances0 or 8fluids02 & s9ce no *ange 9 weight c\ld be discov]$ 9 a body :5 x 0 electrifi$1 x 01 9 g5]al1 assum$ t ! electric fluids 7 weightless4 ,9 ! normal1 neutral body x 0 believ$ t ^! fluids 7 mix$ 9 equal quantities1 !reby neutraliz+ ea* o!r2 on ?is acc\nt !y 7 suppos$ to be ( opposite *>act]i/ics1 s "o 0 call$ positive & ! o!r negative4 ,accord+ to a second !ory1 !re 0 assum$ to be j "o k9d ( electricity1 :i* 0 pres5t 9 a normal am\nt 9 neutral bodies2 positive electricity 0 caus$ by a sup]fluity ( ! fluid2 negative1 by a deficit4 ,9 bo? !ories x 0 possible to talk ( ! am\nt ( positive or negative electricity :i* a body conta9$ or ) :i* x 0 8*>g$10 because ! support]s ( ! "o-fluid idea und]/ood by ! t]ms positive & negative a sup]fluity & a deficit1 respectively1 ( ! "o fluid4 ,9 bo? !ories x 0 possible to talk ab\t ! direction ( ! electric curr5t 9 a conductor1 s9ce ! support]s ( ! two-fluid !ory und]/ood by 8direction0 t 9 :i* ! electric =ces s5t ! positive electricity1 or ! opposite to t 9 :i* ! negative w\ld be s5t4 ,x c\ld n be decid$ :e!r positive electricity w5t 9 ! "o direction or ! negative 9 ! o!r1 or :e!r ea* simultane\sly mov$ 9 its own direction4 ,bo? !ories 7 q arbitr>y 9 designat+ ! electric *>ge 9 glass1 :i* 0 rubb$ ) wooll5 clo?1 z positive4 ,on ! :ole1 nei!r !ory seem$ to h any ess5tial advantage ov] ! o!r2 ! diff]5ce betwe5 !m seem$ to lie m 9 phraseology ?an 9 actual fact4 ,t ! positive & negative /ates ( electricity c\ld n be tak5 z 8symmetric0 seem$1 h[ev]1 to foll[ f ! s-call$ dis*>ge ph5om5a1 9 :i* electricity1 ) ! emission ( light1 /reams out into ! air f /rongly *>g$ 7positive or negative7 bodies1 or passes ?r\gh ! air betwe5 positive & negative bodies 9 sp>ks1 electric arcs or 9 "s o!r way4 ,9 a dis*>ge 9 air betwe5 a metal po9t & a metal plate1 = in/ance1 a bu%-%ap$ gl[ is se5 to ext5d f ! po9t :5 ! *>ge !re is positive1 :ile only a little /> appe>s :5 ! *>ge is negative4 ,naturally1 we _c discuss "h ! _m electric ph5om5a & laws1 & mu/ be satisfi$ ) a brief description ( ^? :i* are ( importance 9 ! atomic !ory4 ,9 ?is latt] category belongs ,c\lomb's ,law1 =mulat$ ab\t #aghe4 ,accord+ to ?is law1 ! repulsions or attractions betwe5 two electrically *>g$ bodies are directly z ! product ( ! *>ges & inv]sely z ! squ>e ( ! di/ance betwe5 !m 7z 9 ! case ( ! gravitational attraction betwe5 two neutral bodies1 accord+ to ,newton's ,law74 ,! unit 9 measur+ electric *>ges c be tak5 z t am\nt :i* w repel an equal am\nt ( electricity ( ! same k9d at unit di/ance ) unit =ce4 ,if we use ! sci5tific or 8absolute0 sy/em1 9 :i* ! unit ( l5g? is "o c5timetre1 t ( "t "o second & t ( mass "o gram1 !n ! unit ( =ce is "o dyne1 :i* is a little great] ?an ! e>?'s attraction on a milligram weight4 ,let u suppose t two small bodies ) equal *>ges ( positive 7or negative7 electricity are at a di/ance ( "o c5timetre f ea* o!r4 ,if !y repel ea* o!r ) a *>ge ( "o dyne1 !n ! am\nt ( electricity ) :i* ea* is *>g$ is call$ ! absolute electro/atic unit ( electricity4 ,if "o body has a *>ge ?ree times z great & ! o!r has a *>ge f\r times z great1 ! repulsion is #c #d #ab times great]4 ,if ! di/ance betwe5 ! bodies is increas$ f "o to five1 ! repulsion is tw5ty-five times z small1 s9ce #e #be4 ,if ! *>ge ( "o body is sub/itut$ by a negative "o ( same magnitude ! repulsion becomes an attraction ( ! same magnitude4 ,9 ! e>ly "p ( ! n9ete5? c5tury me?ods 7 f\nd = produc+ a /eady electric curr5t 9 metal wires4 ,9 #ahbj1 ! ,dani% physici/1 ,h4 ,c4 r/$1 discov]$ t an electric curr5t influ5ces a magnet 9 a *>act]i/ic way1 & t1 conv]sely1 ! curr5t is affect$ by ! =ces emanat+ f ! magnet1 by a magnetic field 9 o!r words4 ,! ,fr5* sci5ti/1 ,ampre1 soon aft]w>ds =mulat$ exact laws = ! electromagnetic =ces betwe5 magnets & curr5ts4 ,9 #ahca1 ! ,engli% physici/1 ,f>aday1 discov]$ t an electric curr5t is induc$ 9 a wire :5 curr5ts or magnets 9 its neighb\rhood are mov$ or *ange /r5g?4 ,f>aday's views on electric & magnetic fields ( =ce ar\nd curr5ts & magnets 7 fur!r ( fundam5tal importance to ! electromagnetic wave !ory z develop$ by ,maxwell4 ,! bran* ( physics deal+ ) all ^! ph5om5a is n[ g5]ally kn[n z electrodynamics4 ,illu/ration3 ,,fig4 #ad4--,picture ( electrolysis ( hydrog5 *loride4 ,a1 anode2 ,k1 ca?ode2 ,h1 hydrog5 atoms2 ,cl1 *lor9e atoms4 ,electrolysis4 ,f>aday also /udi$ ! *emical effects :i* an electric curr5t produces ^u be+ conduct$ betwe5 two metal plates1 call$ electrodes1 :i* are imm]s$ 9 a solution ( salts or acids4 ,! curr5t sep>ates ! salt or acid into two p>ts :i* are c>ri$ by ! electric =ces 9 two opposite directions4 ,?is sep>ation is call$ electrolysis4 ,if ! liquid is dilute hydro*loric acid 7,h,cl71 ! hydrog5 goes ) ! curr5t to ! negative electrode1 ! ca?ode1 & takes ! positive electricity ) x1 :ile ! *lor9e goes aga9/ ! curr5t & takes ! negative electricity to ! positive electrode1 ! anode4 ,we mu/ !n assume ) ! ,sw$i% sci5ti/1 ,arrh5ius1 t1 "u ! influ5ce ( ! wat]1 ! molecules ( hydrog5 *loride always are sep>at$ into positive hydrog5 atoms & negative *lor9e atoms1 & t ! electric =ces f ! anode & ! ca?ode c>ry ^! atoms respectively ) & aga9/ ! curr5t4 ,! electrically *>g$ w&]+ atoms are call$ ions1 i4e4 w&]]s4 ,! positive electricity tak5 by ! hydrog5 atoms to ! ca?ode goes into ! metal conductor1 :ile ! anode mu/ receive f ! metal conductor an equal am\nt ( positive electricity to be giv5 to ! *lor9e atoms to neutralize !m4 ,! negative *>ge ( a *lor9e atom mu/ !n be z l>ge z ! positive *>ge ( a hydrog5 atom4 ,^! assumptions imply t equal numb]s ( ! two k9ds ( atoms are pres5t 9 ! :ole quantity ( atoms transf]r$ 9 any p]iod ( "t4 ,f>aday f\nd t ! quantity ( hydrog5 :i* 9 ! above exp]im5t is transf]r$ to ! ca?ode 9 a giv5 "t is proportional to ! quantity ( electricity transf]r$ 9 ! same "t4 ,a gram ( hydrog5 always takes ! same am\nt ( electricity ) x4 ,by exp]im5t ?is am\nt ( electricity c be det]m9$1 &1 s9ce ! weight 9 grams ( ! hydrog5 atom is kn[n1 x is possible to calculate ! am\nt ( "o atom4 ,9 electro/atic units x is #dgg #aj1 i4e41 #dgg billion?#a p>ts4 ,a *lor9e atom !n c>ries ) x #dgg #aj electro/atic units ( negative electricity4 ,s9ce its atomic weight is #cee1 !n #cee grams ( *lor9e w take z mu* electricity z #a gram ( hydrog54 ,! ratio e_/m betwe5 ! *>ge e & ! mass m is !n #cee times z great = hydrog5 z = *lor9e4 #a ,billion us$ "h to mean "o million million1 & trillion to mean "o million billion4 ,we h tempor>ily re/rict$ ourselves to ! electrolysis ( hydrog5 *loride4 ,let u n[ assume t we h *loride ( z9c 7,zn,cl71 :i*1 by electrolysis1 is sep>at$ into *lor9e & z9c4 ,ea* atom ( *lor9e w1 z be=e1 c>ry #dgg #aj units ( negative electricity to ! anode2 b s9ce z9c is dival5t 7cf4 p4 #ag7 & "o atom ( z9c is jo9$ to two ( *lor9e1 !re=e "o atom ( z9c mu/ c>ry a *>ge ( #b #dgg #aj units ( positive electricity to ! ca?ode4 ,an atom or a gr\p ( atoms1 ) val5ce ( ?ree1 9 electrolysis c>ries #c #dgg #aj units1 etc4 ,we see !n1 t ! quantity ( electricity :i* accompanies ! atoms 9 electrolysis is always #dgg #aj electro/atic units or an integral multiple !re(4 ,?is sugge/s ! ?\ght t electricity is atomic & t ! quantity #dgg #aj units is ! smalle/ am\nt ( electricity :i* c exi/ indep5d5tly1 i4e41 ! elem5t>y quantum ( electricity or ! 8atom ( electricity40 ,! atom ( a monoval5t elem5t1 :5 *>g$ or ioniz$1 %\ld h "o atom ( electricity2 a dival5t1 two1 etc4 ,on ! two-fluid !ory x 0 mo/ reasonable to assume t !re 7 two k9ds ( atoms ( electricity repres5t+1 respectively1 positive & negative electricity4 ,9 ,fig4 #ae !re is giv51 9 accordance ) ! two-fluid !ory1 a r\gh picture ( a *lor9e ion & a hydrog5 ion & _! union into a molecule4 ,illu/ration3 ,,fig4 #ae4--,provisional repres5tation 7accord+ to ! two-fluid !ory7 ( ,a1 a hydrog5 ion2 ,b1 a *lor9e ion2 & ,c1 a molecule ( hydrog5 *loride4 ,! atoms ( electricity seem$ to diff] ess5tially f ! usual atoms ( ! elem5ts 9 _! app>5t inability to live indep5d5tly2 !y seem$ to exi/ only 9 connection ) ! atoms ( ! elem5ts4 ,!y w\ld seem mu* m real if !y c\ld exi/ indep5d5tly4 ,t su* exi/5ce really is possible1 has be5 discov]$ by ! /udy ( ! motion ( electricity 9 gases4 ,vacuum ,tube ,ph5om5a4 ,illu/ration3 ,,fig4 #af4--,vacuum tube ) ca?ode rays & a %ad[-produc+ cross4 ,p & ,n1 conduct+ wires = ! electric curr5t2 a1 ca?ode2 b1 anode & %ad[-produc]2 c1 d1 ! %ad[4 ,illu/ration3 ,,fig4 #ag4--,vacuum tube1 :]e a bundle ( ca?ode rays are deviat$ by electric =ces4 ,a1 anode2 ,k1 ca?ode4 ,x has previ\sly be5 said t air is an insulator = electricity1 a /atem5t :i* is1 9 g5]al1 true2 h[ev]1 z has also be5 said1 electric sp>ks & arcs c pass ?r\gh air4 ,moreov]1 x has be5 discov]$ t exhau/$ air is a v good conductor1 s t a /rong curr5t c pass betwe5 two metal electrodes 9 a glass tube :]e ! air is exhau/$1 if ! electrodes are connect$ to an out] conductor by metal wires fus$ into ! glass4 ,9 ^! vacuum tubes !re are produc$ rem>kable light effects1 at fir/ inexplicable4 ,:5 ! air is v mu* exhau/$1 to a hundr$ ?\s&? ( ! atmosph]ic pressure or less1 /rong electric =ces 7l>ge diff]5ce ( pot5tial betwe5 ! electrodes7 are ne$$ to produce an electric dis*>ge4 ,su* a dis*>ge assumes an entirely new "*2 9 ! int]ior ( ! glass tube !re is h>dly any light to be se51 b ! glass wall opposite ! negative electrode 7! ca?ode7 gl[s ) a gre5i% t9t 7fluoresc5ce74 ,if a small metal plate is put 9 ! tube betwe5 ! ca?ode & ! glass wall1 a %ad[ is ca/ on ! wall1 j z if light 7 produc$ by rays1 emitt$ f ! ca?ode at "r angles to its surface 7cf4 ,fig4 #af74 ,! ,engli% physici/1 ,crookes1 0 "o ( ! fir/ to /udy ^! ca?ode rays4 ,he assum$ t !y are n e!r waves l ! light rays1 b t !y consi/ ( p>ticles :i* are hurl$ f ! ca?ode ) great velocity 9 /raight l9es2 !y light ! wall by _! collisions ) x4 ,!re 0 soon no d\bt z to ! correctness ( ,crookes' !ory4 ,! ca?ode rays are evid5tly p>ticles ( negative electricity1 :i* by repulsions are driv5 f ! ca?ode 7! negative electrode74 ,a metal plate bomb>d$ by ! rays becomes *>g$ negatively4 ,let u suppose t we h a small bundle ( ca?ode rays1 obta9$ by pass+ ! rays f ! ca?ode ,k 7cf4 ,fig4 #ag7 ?r\gh two n>r[ op5+s ,s & ,s4 ,x c !n be %[n t ! bundle ( rays is deviat$ n only by electric =ces1 b also by magnetic action f a magnet :i* is held ne> ! glass4 ,9 ! figure !re is %[n a deviation ( ! k9d m5tion$1 caus$ by mak+ ! plates at ,b & ,c respectively positive & negative2 s9ce ,b attracts ! negative p>ticles & ,c repels !m1 ! light spot produc$ by ! bundle ( rays is mov$ f ,m to ,m4 ,! magnetic deviation is 9 agreem5t ) r/$'s rules = ! reciprocal actions betwe5 curr5ts & magnets1 if we consid] ! bundle ( rays produc$ by mov+ electric p>ticles z an electric curr5t4 7,s9ce ! electric p>ticles travell+ 9 ! direction ( ! rays are negative1 & s9ce x is cu/om>y by ! expression 8direction ( curr5t0 to und]/& ! direction opposite to t 9 :i* ! negative electricity moves1 !n1 9 ! case ( ! ca?ode rays j m5tion$1 ! direction ( ! curr5t mu/ be opposite to t ( ! rays47 ,f measurem5ts ( ! magnetic & electric deviations x is possible to f9d n only ! velocity ( ! p>ticles1 b also ! ratio e_/m betwe5 ! *>ge e ( ! p>ticle & its mass m4 ,! velocity v>ies ) ! pot5tial at ! ca?ode1 & may be v great1 #ej1jjj km4 p] second1 = in/ance 7ab\t "o-six? ! spe$ ( light71 or m4 ,x has be5 f\nd t e_/m always has ! same value1 reg>dless ( ! metal ( ! ca?ode & ( ! gas 9 ! tube2 ?is means t ! p>ticles are n atoms ( ! elem5ts1 b some?+ q new4 ,x has also be5 f\nd t e_/m is ab\t two ?\s& times z l>ge z ! ratio betwe5 ! *>ge & ! mass ( ! hydrog5 atom 9 electrolysis4 ,if we n[ assume t e is j ! elem5t>y quantum ( electricity #dgg #aj1 :i* 9 magnitude am\nts to ! *>ge ( ! hydrog5 atom 9 electrolysis 7b is negative71 !n m mu/ h ab\t _/ ! mass ( ! hydrog5 atom4 ,?is assumption z to ! size ( e has be5 ju/ifi$ by exp]im5ts ( m direct nature4 ,! exp]im5ts ) *>ge & mass ( electrons :i* h 9 p>ticul> be5 c>ri$ out by ! ,engli% physici/1 ,j4 ,j4 ,?omson1 give reason !n to suppose ^! q new & unkn[n p>ticles to be free atoms ( negative electricity2 !y h be5 giv5 ! "n ( electrons4 ,gradually m in=mation ab\t !m has be5 acquir$4 ,?us x has be5 possible 9 v>i\s ways to det]m9e directly ! *>ge on ! electron1 indep5d5tly ( its mass4 ,special m5tion mu/ be made ( ! brilliant inve/igations ( ! ,am]ican1 ,millikan1 on ! motion ( v small electrifi$ oil-drops ?r\gh air "u ! influ5ce ( an electric =ce4 ,to ,millikan is due ! above-m5tion$ value ( e1 :i* is accurate to "o "p 9 five hundr$4 ,fur!r1 ! mass ( ! electron has be5 m exactly calculat$ z ab\t _/ t ( ! hydrog5 atom4 ,_! magnitude has also be5 le>n$2 ! radius ( ! electron is e/imat$ z #ae #aj cm4 or #ae #aj 1 an ord] ( magnitude "o t5-?\s&? t ( ! molecule or atom4 ,aft] ! atom ( negative electricity _h be5 isolat$1 9 ! =m ( ca?ode rays1 ! next sugge/ion 0 t correspond+ positive electric p>ticles might be dis*>g$ f ! anode 9 a vacuum tube4 ,by special me?ods success has be5 atta9$ 9 %[+ & /udy+ rays ( positive p>ticles4 ,9 ord] to sep>ate !m f ! negative ca?ode ray p>ticles ! ,g]man sci5ti/1 ,gold/e91 let ! positive p>ticles pass ?r\gh canals 9 ! ca?ode2 !y are !re=e call$ canal rays4 ,! velocity ( ! p>ticles is mu* less ?an t ( ! ca?ode rays1 & ! ratio e_/m betwe5 *>ge & mass is mu* small] & v>ies accord+ to ! gas 9 ! tube4 ,9 exp]im5ts :]e ! tube conta9s hydrog51 rays are always f\nd = :i* e_/m1 z 9 electrolysis1 is ab\t _/ ( ! ratio 9 ! ca?ode rays4 ,!re=e !re c be sc>cely any d\bt t ^! canal rays are made up ( *>g$ hydrog5 atoms or hydrog5 ions4 ,! values f\nd ) o!r gases indicate t ! p>ticles are atoms 7or molecules sometimes7 ( ! elem5ts 9 "q1 ) *>ges "o or m times ! elem5t>y quantum ( electricity 7#dgg #aj electro/atic units74 ,rese>* 9 ?is field has also be5 due 9 p>ticul> to ,j4 ,j4 ,?omson4 ,f 8 results1 z well z f ^? obta9$ by o!r me?ods1 x foll[s t positive electricity1 unlike negative1 _c appe> ( its own accord1 b is inextricably connect$ to ! atoms ( ! elem5ts4 ,! ,nature ( ,electricity4 ,! e>li] conceptions ( a "o or two-fluid explanation ( ! ph5om5a ( electricity appe> n[ 9 a new light4 ,we are l$ to ?9k ( a neutral atom z consi/+ ( "o mass *>g$ ) positive electricity toge!r ) z _m electrons negatively *>g$ z are suffici5t to neutralize ! positive4 ,if ! atom loses "o1 two or ?ree electrons1 x becomes positive ) a *>ge ( "o1 two or ?ree elem5t>y quanta ( electricity1 or = ! sake ( simplicity & brevity we say t ! atom has "o1 two or ?ree 8*>ges40 ,if1 on ! o!r h&1 x takes up "o1 two or ?ree extra electrons x has "o1 two or ?ree negative *>ges4 ,fig4 #ah c give help 9 und]/&+ ^! ideas1 b x mu/ n be ?\ght t ! electrons are arrang$ 9 ! way indicat$4 ,! sub/ances1 :i* appe> z electropositive 9 electrolysis--i4e4 hydrog5 & metals--%\ld !n be su* t _! atoms easily lose "o or m electrons1 :ile ! electronegative elem5ts %\ld1 on ! o!r h&1 easily take up extra electrons4 ,elem5ts %\ld be monoval5t or dival5t accord+ z _! atoms are apt to lose or to take up "o or two electrons4 ,f inve/igations ) ! vacuum tube x appe>s1 h[ev]1 t ! atoms ( ! same elem5t c 9 ?is respect behave 9 m ways ?an w\ld be expect$ f electrolysis or *emical val5ce4 ,illu/ration3 ,,fig4 #ah4--,provisional repres5tation 7accord+ to ! electron !ory7 ( ,a1 a neutral atom2 ,b1 ! same atom ) two positive *>ges 7a dival5t positive ion7 & ,c1 ! same atom ) two negative *>ges 7a dival5t negative ion74 ,:5 an electric curr5t passes ?r\gh a metal wire1 x mu/ be assum$ t ! atoms ( ! metal rema9 9 place1 :ile ! electrical =ces c>ry ! electrons 9 a direction opposite to t :i* usually is consid]$ z ! direction ( ! curr5t 7cf4 p4 #gj74 ,! motion ( ! electrons mu/ n be suppos$ to proce$ )\t h9drance1 b r z ! result ( a complicat$ int]play1 by no means completely und]/ood1 :]eby ! electrons are fre$ f & caught by ! atoms & travel backw>ds & =w>ds1 9 su* a way t ?r\gh e section ( ! metal wire a surplus ( electrons is /eadily pass+ 9 ! direction opposite to ! s-call$ direction ( ! curr5t4 ,! numb] ( surplus electrons :i* 9 e second passes ?r\gh a section ( ! ?9 metal wire 9 an ord9>y tw5ty-five c&le inc&esc5t light1 at #bbj volts1 am\nts to ab\t "o trillion 7#aj71 or #ajjj million 7#aj7 9 #jjjj1jjj1jja ( a second4 ,if ! metal conduct+ wire ends 9 ! ca?ode ( a vacuum tube1 ! electrons c>ri$ ?r\gh ! wire pass freely into ! tube z ca?ode rays f ! ca?ode4 ,?is motion ( electricity agrees be/ ) ! "o-fluid !ory1 s9ce ! electrons1 :i* "h alone accompli% ! passage ( ! electricity1 may be consid]$ z ! fundam5tal p>ts ( electricity4 ,9 ?is respect ! *oice ( ! t]ms positive & negative is v un=tunate1 s9ce a body ) a negative *>ge actually has a surplus ( electrons4 ,moreov]1 ! electrons really h mass2 b s9ce ! mass ( a s+le electron is only _/ t ( ! atom ( ! lighte/ elem5t1 hydrog51 & s9ce 9 an electrifi$ body :i* c be weigh$ by scale !re is always b an inf9itesimal numb] ( *>g$ atoms1 x is easy to und]/& t1 =m]ly1 electricity seem$ to be )\t weight4 ,9 electrolysis1 :]e ! motion ( electricity is accompli%$ by positive & negative ions1 we h a clos] connection ) ! two-fluid !ory4 ,9 motions ( electricity ?r\gh air ! situation sugge/s bo? ! "o-fluid & ! two-fluid !ories1 s9ce ! passage ( electricity is sometimes c>ri$ on exclusively by ! electrons1 & sometimes p>tly by !m & p>tly by l>g] positive & negative ions1 i4e41 atoms or molecules ) positive & negative *>ges4 ,! ,electron ,!ory4 ,proce$+ on ! assumption t ! electric & optical prop]ties ( ! elem5ts are det]m9$ by ! activity ( ! electric p>ticles1 ! ,dut* physici/ ,lor5tz & ! ,engli% physici/ ,l>mor succe$$ 9 =mulat+ an extraord9>ily compreh5sive 8electron !ory10 by :i* ! electrodynamic laws = ! v>iations 9 /ate ( ! e!r 7 adapt$ to ! doctr9e ( ions & electrons4 ,?is ,lor5tz !ory mu/ be recogniz$ z "o ( ! f9e/ & mo/ significant results ( n9ete5? c5tury physical rese>*4 ,x 0 "o ( ! mo/ sugge/ive problems ( ?is !ory to acc\nt = ! emission ( light waves f ! atom4 ,f ! previ\sly describ$ electromagnetic !ory ( light 7cf4 p4 #db7 x foll[s t an electron oscillat+ 9 an atom w emit light waves 9 ! e!r1 & t ! frequ5cy ( ^! waves w naturally be equal to ! numb] ( oscillations ( ! electron 9 a second4 ,if ?is la/ quantity is designat$ z 1 !n ,x may !n be suppos$ t ! electrons 9 ! undi/urb$ atom are 9 a /ate ( re/1 comp>able ) t ( a ball 9 ! bottom ( a b[l4 ,:5 ! atom 9 "s way is 8%ak510 "o or m ( ! electrons 9 ! atom beg9s to oscillate ) a def9ite frequ5cy1 j z ! ball might roll back & =? 9 ! b[l if ! b[l 0 %ak54 ,?is means t ! atom is emitt+ light waves1 :i*1 = ea* individual electron h a def9ite wave-l5g? correspond+ to ! frequ5cy ( ! oscillations1 & t1 9 ! spectrum ( ! emitt$ light1 ! obs]v$ spectral l9es correspond to ^! wave-l5g?s4 ,/rong support = ?is view 0 af=d$ by ,zeeman's discov]y ( ! influ5ce ( a magnetic field ^u spectral l9es4 ,zeeman1 a ,dut* physici/1 discov]$1 ab\t tw5ty-five ye>s ago1 t :5 a gl[+ vacuum tube is plac$ betwe5 ! poles ( a /rong electromagnet1 ! spectral l9es 9 ! emitt$ light are split s t ea* l9e is divid$ into ?ree compon5ts ) v little di/ance betwe5 !m4 ,x 0 "o ( ! great triumphs ( ! electron !ory t ,lor5tz 0 able to %[ t su* an effect 0 to be expect$ if x 0 assum$ t ! oscillations ( light 7 produc$ by small oscillat+ electric p>ticles )9 ! atom4 ,f ! exp]im5ts & f ! kn[n laws conc]n+ ! reciprocal actions ( a magnet & an electric curr5t 7"h ! mov+ p>ticle71 ! !ory enabl$ ,lor5tz to f9d n only ! ratio e_/m betwe5 ! electric *>ge ( ea* ( ^! p>ticles & its mass1 b also ! nature ( ! *>ge4 ,he c\ld conclude f ,zeeman's exp]im5t t ! *>ge is negative & t ! ratio e_/m is ! same z t f\nd = ! ca?ode rays4 ,aft] ?is !re c\ld n well be d\bt t ! electrons 9 ! atoms 7 ! orig9 ( ! light :i* gives ! l9es ( ! spectrum4 ,x seem$1 h[ev]1 q unfeasible = ! !ory to expla9 ! details 9 a spectrum--to d]ive1 = in/ance1 ,balm]'s =mula1 or to %[ :y hydrog5 has ^! l9es1 copp] ^?1 etc4 ,^! difficulties1 comb9$ ) ! great numb] ( l9es 9 ! diff]5t spectra1 seem$ to mean t !re 7 _m electrons 9 an atom & t ! /ructure ( an atom 0 exce$+ly complicat$4 ,ionization by ,x-rays & ,rays f ,radium4 ,radioactivity4 ,z has be5 said1 ! electrons 9 a vacuum tube cause its wall to emit a gre5i% light :5 !y /rike x4 ,^u meet+ ! glass wall or a piece ( metal 7! antica?ode7 plac$ 9 ! tube ! electrons cause also ! emission ( ! peculi>1 p5etrat+ rays call$ ,rntg5 rays 9 hon\r ( _! discov]]1 or m commonly ,x-rays4 ,!y may be describ$ z ultra-violet rays ) exce$+ly small wave-l5g?s 7cf4 p4 #ed74 ,:51 fur!r1 ! electrons meet gas molecules 9 ! tube !y break !m to pieces1 sep>at+ !m into positive & negative ions 7ionization74 ,! positive ions are ! ones :i* appe> 9 ! canal rays4 ,! ions set 9 motion by electrical =ces c break o!r gas molecules to pieces1 ?us assi/+ 9 ! ionization process4 ,at ! same "t ! gas molecules & atoms are made to produce di/urbances 9 ! e!r1 & ?us to cause ! light ph5om5a :i* arise 9 a tube :i* is n too /rongly exhau/$4 ,! free air c be ioniz$ 9 v>i\s ways2 ?is ionization c be detect$ because ! air becomes m or less conduct+4 ,9 fact1 electric =ces w drive ! positive & negative ions ?r\gh ! air 9 opposite directions1 ?us giv+ rise to an electric curr5t4 ,if ! ionization process is n /eadily cont9u$1 ! air gradually loses its conductivity1 s9ce ! positive & negative ions recomb9e into neutral atoms or molecules4 ,ionization c be produc$ by flames1 s9ce ! air ris+ f a flame conta9s ions4 ,a /rong ionization c also be br\ght ab\t by ,x-rays & by ultra-violet rays4 ,9 ! high] /rata ( ! atmosph]e ! ultra-violet rays ( ! sun ex]cise an ioniz+ influ5ce4 ,mo/ ( all1 h[ev]1 ! air is ioniz$ by rays f ! s-call$ radioactive sub/ances :i* 9 v small quantities are di/ribut$ ab\t ! _w4 ,! *>act]i/ic radiation f ^! sub/ances 0 discov]$ 9 ! la/ decade ( ! n9ete5? c5tury by ! ,fr5* physici/1 ,becqu]el1 & aft]w>ds /udi$ by ,m4 & ,mme4 ,curie4 ,f ! radioactive uranium m9]al1 pit*bl5de1 ! latt] sep>at$ ! _m times m /rongly radioactive elem5t radium4 ,! prop] nature ( ! rays 0 lat] expla9$1 p>ticul>ly ?r\gh ! inve/igations ( ! ,engli% physici/s1 ,ru!r=d1 ,soddy & ,ramsay4 ,^! rays1 :i* c produce heat effects1 photographic effects & ionization1 are ( ?ree q diff]5t classes1 & accord+ly are kn[n z -rays1 -rays1 & -rays4 ,! la/ nam$1 l ! ,x-rays1 are ultra-violet rays1 b !y h (t5 ev5 %ort] wave-l5g?s & a mu* great] p[] ( p5etration ?an ! usual ,x-rays4 ,! -rays are electrons :i* are eject$ ) mu* great] velocity ?an ! ca?ode rays2 9 "s cases _! velocity goes up to #iih p] c5t4 t ( light4 ,! -rays are positive atomic ions1 :i* move ) a velocity v>y+ accord+ to ! emitt+ radioactive elem5t f _/ to almo/ _/ t ( light4 ,x has fur!r be5 prov$ t ! -p>ticles are atoms ( ! elem5t helium1 :i* has ! atomic weight #d1 & t !y possess two positive *>ges1 i4e41 !y mu/ take up two electrons to produce a neutral helium atom4 ,!re is no d\bt t ! process :i* takes place 9 ! emission ( radiation f ! radioactive elem5ts is a trans=mation ( ! elem5t1 an explosion ( ! atoms accompani$ by ! emission ei!r ( d\ble-*>g$ helium atoms or ( electrons1 & ! =m+ ( ! atoms ( a new elem5t4 ,! en]gy ( ! rays is an int]nal atomic en]gy1 fre$ by ^! trans=mations4 ,! elem5t uranium1 ) ! greate/ ( all kn[n atomic weights 7#bch71 passes1 by sev]al int]m$iate /eps1 into radium ) atomic weight #bbf2 f radium !re comes1 aft] a s]ies ( /eps1 lead1 or1 9 any case1 an elem5t :i*1 9 all its *emical prop]ties1 behaves l lead4 ,we %all g no fur!r into ?is subject1 m]ely rem>k+ t ! trans=mations are q indep5d5t ( ! *emical comb9ations into :i* ! radioactive elem5ts h ent]$1 & ( all ext]nal influ5ces4 ,:5 -p>ticles f radium are s5t aga9/ a scre5 ) a coat+ ( especially prep>$ z9c sulphide1 on ?is scre51 9 ! d>k1 !re c be se5 a *>act]i/ic light ph5om5on1 ! s-call$ sc9tillation1 :i* consi/s ( _m fla%es ( light4 ,ea* individual fla% means t an -p>ticle1 a helium atom1 has hit ! scre54 ,9 ?is bomb>dm5t by atoms ! individual atom-projectiles are made visible 9 a mann] simil> to t 9 :i* ! individual ra9drops :i* fall on ! surface ( a body ( wat] are made visible by ! wave r+s :i* spread f ! places :]e ! drops meet ! wat]4 ,?is fla% ( light 0 ! fir/ effect ( ! individual atom to be available = inve/igation & obs]vation4 ,! incr$ibility ( any?+ s small z an atom produc+ a visible effect is less5$ :51 in/ead ( pay+ att5tion m]ely to ! small size or mass ( ! atom1 its k9etic en]gy is consid]$2 ?is en]gy is proportional to ! squ>e ( ! velocity1 :i* is "h ( ov]:elm+ magnitude4 ,= ! mo/ rapid -p>ticles ! velocity is #bbf #aj cm4 p] second2 _! k9etic en]gy is !n ab\t _/ ( ! k9etic en]gy ( a weight ( "o milligram ( a sub/ance at a velocity ( "o c5timetre p] second4 ,?is en]gy may seem v small1 b1 at lea/1 x is n a magnitude ( 8inconceivable m9ut5ess10 & x is suffici5t "u ! conditions giv5 above to produce a visible light effect4 ,we mu/ "h also consid] ! extreme s5sitiv5ess ( ! eye4 ,illu/ration3 ,,fig4 #ai4--,photograph ( pa?s describ$ by -p>ticles 7positive helium ions7 emitt$ f a radioactive sub/ance4 ,m practical me?ods ( reveal+ ! effects ( ! individual -p>ticles & ( c\nt+ !m are f\nd$ on _! v /rong ionization p[]4 ,by /r5g!n+ ! ionization p[] ( -p>ticles1 ,ru!r=d & ,geig] 7 able to make ! air 9 a s-call$ ionization *amb] s good a conductor t an individual -p>ticle caus$ a deflection 9 an electrical app>atus1 an electrometre4 ,illu/ration3 ,,fig4 #bj4--,photograph ( ! pa? ( a -p>ticle 7an electron74 7,bo? #ai & #bj are photographs by ,c4 ,t4 ,r4 ,wilson47 ,) a m direct me?od ! ,engli% sci5ti/ ,c4 ,t4 ,r4 ,wilson has %[n ! pa?s ( ! -p>ticles by mak+ use ( ! *>act]i/ic prop]ty ( ions1 t 9 damp air !y attract ! neutral wat] molecules :i* !n =m drops ( wat] ) ! ions z nuclei4 ,9 air :i* is completely free ( du/ & ions ! wat] vap\r is n cond5s$1 ev5 if ! temp]ature is decreas$ s z to give rise to sup]saturation1 b z soon z ! air is ioniz$ ! vap\r cond5ses into a fog4 ,:5 ,wilson s5t -p>ticles ?r\gh air1 sup]saturat$ ) wat] vap\r1 ! vap\r cond5s$ into small drops on ! ions produc$ by ! p>ticles2 ! /reaks ( fog ?us obta9$ c\ld be photograph$4 ,fig4 #ai %[s su* a photograph ( ! pa?s ( a numb] ( atoms4 ,:5 a /reak ( fog ends abruptly x does n mean t ! -p>ticles h sudd5ly halt$1 b t _! velocity has decreas$ s t !y c no long] break ! molecules ( air to pieces1 produc+ ions4 ,! pa?s ( ! -p>ticles h be5 photograph$ 9 ! same way1 al?\gh an electron ( ! -p>ticles has a mass ab\t #gjjj times small] ?an t ( a helium atom2 ! electron has1 h[ev]1 a f> great] velocity ?an ! helium atom4 ,?is velocity causes ! ions to be f>!r ap>t1 s t ea* drop ( wat] =m$ ar\nd ! individual ions c appe> 9 ! photograph by itself 7cf4 ,fig4 #bj74 ,,*apt] ,,iv ,,! ,,nucle> ,,atom ,introduction4 ,we are n[ br\ght face to face ) ! fundam5tal "q1 h>dly t\*$ ^u at all 9 ! previ\s "p ( ?is "w1 namely1 t ( ! con/ruction & mode ( op]ation ( ! atomic me*anism itself4 ,9 ! fir/ place we mu/ ask3 ,:at is ! 8ar*itecture0 ( ! atom1 t is1 :at positions d ! positive & negative p>ticles take up ) respect to ea* o!r1 & h[ _m are !re ( ea* k9d8 ,9 ! second place1 ( :at sort are ! processes :i* take place 9 an atom1 & h[ c we make !m int]pret ! physical & *emical prop]ties ( ! elem5ts8 ,9 ?is *apt] we %all keep ess5tially to ! fir/ "q1 & consid] especially ! great contribution :i* ,ru!r=d made 9 #aiaa to its answ] 9 8 discov]y ( ! positive atomic nucleus & 9 ! developm5t ( :at is kn[n z ! ,ru!r=d atomic model or nucle> atom4 ,ru!r=d's ,atom ,model4 ,ru!r=d's discov]y 0 ! result ( an inve/igation :i*1 9 its ma9 outl9es1 0 c>ri$ out z foll[s3 a d5se /ream ( -p>ticles f a p[]ful radium prep>ation 0 s5t into a highly exhau/$ *amb] ?r\gh a little op5+4 ,on a z9c sulphide scre51 plac$ a little di/ance beh9d ! op5+1 !re 0 !n produc$ by ?is bomb>dm5t ( atomic projectiles1 a small1 %>ply def9$ spot ( light4 ,! op5+ 0 next cov]$ by a ?9 metal plate1 :i* c be consid]$ z a piece ( *a9 mail =m$ ( d5sely-pack$ atoms4 ,! -p>ticles1 work+ _! way ?r\gh ! atoms1 easily trav]s$ ?is 8piece ( mail0 because ( _! great velocity4 ,b n[ x 0 se5 t ! spot ( light broad5$ out a little & 0 no long] %>ply limit$4 ,f ?is fact "o c\ld conclude t ! -p>ticles 9 pass+ among ! _m atoms 9 ! metal plate suff]$ c\ntless1 v small deflections1 ?us produc+ a slight spread+ ( ! rays4 ,x c\ld also be se5 t "s1 ?\gh comp>atively few1 ( ! -p>ticles broke utt]ly away f ! /ream1 & travell$ f>!r 9 new directions1 "s1 inde$1 glanc+ back f ! metal plate 9 ! direction 9 :i* !y _h come 7cf4 ,fig4 #ba74 ,! situation 0 approximately z if "o _h dis*>g$ a quantity ( small %ot ?r\gh a wall ( butt]1 & ne>ly all ! pellets _h gone ?r\gh ! wall 9 an almo/ un*ang$ direction1 b t "o or two individual ones _h 9 "s app>5tly uncall$ = fa%ion come travell+ back f ! int]ior ( ! butt]4 ,"o might naturally conclude f ?is circum/ance t "h & !re 9 ! butt] 7 locat$ "s small1 h>d1 heavy objects1 = example1 "s small pellets ) :i* "s ( ! projectiles by *ance _h collid$4 ,accord+ly1 x seem$ z if !re 7 locat$ 9 ! metal %eet "s small h>d objects4 ,^! c\ld h>dly be ! electrons ( ! metal atoms1 because -p>ticles1 z has be5 /at$ be=e1 are helium atoms ) a mass ov] sev5 ?\s& times t ( a s+le electron2 & if su* an atom collid$ ) an electron1 x w\ld easily pu% ! electron aside )\t itself be+ deviat$ mat]ially 9 its pa?4 ,h>dly any o!r possibility rema9$ ?an to assume t :at ! -p>ticles _h collid$ ) 0 ! positive "p ( ! atom1 ^: mass is ( ! same ord] ( magnitude z ! mass ( ! helium atom 7cf4 ,fig4 #ba74 ,a ma!matical inve/igation %[$ t ! l>ge deflections 7 produc$ because ! -p>ticles 9 "q _h pass$1 on _! way1 ?r\gh a trem5d\sly /rong electric field ( ! k9d :i* w exi/ ab\t an electric *>ge conc5trat$ into a v small space & act+ on o!r *>ges accord+ to ,c\lomb's ,law4 ,:51 9 ! =ego+1 ! ^w 8collision0 is us$1 x mu/ n be tak5 to mean simply a collision ( ela/ic sph]es2 r ! two p>ticles 7! -p>ticle & ! positive p>ticle ( ! metal atom7 come s ne> to ea* o!r 9 ! flight ( ! =m] t ! v great electrical =ces br\ght into play cause a significant deflection ( ! -p>ticles f _! orig9al c\rse4 ,illu/ration3 ,,fig4 #ba4--,tracks ( -p>ticles 9 ! int]ior ( matt]4 ,:ile #a & #c und]go small deflections by collisions ) electrons1 #b is %>ply deflect$ by a positive nucleus4 ,ru!r=d 0 ?us l$ to ! hypo!sis t ne>ly all ( ! mass ( ! atom is conc5trat$ into a positively *>g$ nucleus1 :i*1 l ! electrons1 is v small 9 comp>ison ) ! size ( ! :ole atom2 :ile ! re/ ( ! mass is apportion$ among a numb] ( negative electrons :i* mu/ be assum$ to rotate ab\t ! nucleus "u ! attraction ( ! latt]1 j z ! planets rotate ab\t ! sun4 ,"u ?is hypo!sis ! out] limits ( ! atom mu/ be reg>d$ z giv5 by ! out]mo/ electron orbits4 ,! assumption ( an atom ( ?is /ructure makes x at once intelligible :y1 9 g5]al1 ! -p>ticles c travel ?r\gh ! atom )\t be+ deflect$ mat]ially by ! nucle> repulsion1 & :y ! v great deflections occur z seldom z is indicat$ by exp]im5t4 ,?is latt] circum/ance has1 on ! o!r h&1 no explanation 9 ! atomic model previ\sly sugge/$ by ,"l ,kelv9 & amplifi$ by ,j4 ,j4 ,?omson1 9 :i* ! positive electricity 0 assum$ to be di/ribut$ ov] ! :ole volume ( ! atom1 :ile ! electrons 7 suppos$ to move 9 r+s at v>y+ di/ances f ! c5tre ( ! atom4 ,illu/ration3 ,,fig4 #bb4--,photograph ( ! pa?s ( two -p>ticles 7positive helium ions74 ,"o collides ) an atomic nucleus4 ,! same *>act]i/ic ph5om5on made evid5t 9 ! passage ( -p>ticles ?r\gh sub/ances by ! inve/igations ( ,ru!r=d appe>s 9 a m direct way 9 ,wilson's rese>*es discuss$ on p4 #ha4 ,8 photographs ( ! pa?s ( -p>ticles ?r\gh air sup]saturat$ ) wat] vap\r 7see ,fig4 #bb7 %[ pron\nc$ k9ks 9 ! pa?s ( individual p>ticles4 ,?us 9 ! figure ref]r$ to1 !re are %[n ! pa?s ( two -p>ticles4 ,"o ( ^! is almo/ a /raight l9e 7) a v slight curvature71 :ile ! o!r %[s a v p]ceptible deflection z x approa*es ! imm$iate neighb\rhood ( ! nucleus ( an atom1 & f9ally a v abrupt k9k2 at ! latt] place x is cle> t ! -p>ticle has p5etrat$ v close to ! nucleus4 ,if "o exam9es ! picture m closely1 !re w be se5 a v small =k at ! place :]e ! k9k is locat$4 ,"h ! pa? seems to h divid$ into two bran*es1 a %ort] & a long]4 ,?is leads "o at once to suspect t a collision betwe5 two bodies has tak5 place1 & t aft] ! collision ea* body has travell$ its own pa?1 j z if1 to return to ! analogy ( ! bomb>dm5t ( ! butt] wall1 "o _h be5 able to drive two pellets out ( ! butt] by %oot+ 9 only "o4 ,or1 to take p]haps a m famili> example1 :5 a mov+ billi>d ball collides at r&om ) a /ation>y "o1 aft] ! collision !y bo? move (f 9 diff]5t directions4 ,s1 :5 ! -p>ticle hits at r&om ! atomic nucleus1 bo? p>ticle & nucleus move (f 9 diff]5t directions2 ?\gh 9 ?is case1 s9ce ! nucleus has ! mu* great] mass ( ! two1 x moves m sl[ly1 aft] ! collision1 ?an ! -p>ticle1 & has1 !re=e1 a mu* %ort] range 9 ! air ?an ! light]1 swift] -p>ticle4 ,_h ! gas 9 :i* ! collisions took place be5 hydrog51 = example1 ! recoil pa?s ( ! hydrog5 nuclei w\ld h be5 long] ?an ^? ( ! -p>ticles1 because ! mass ( ! hydrog5 nucleus is b "o qu>t] ! mass ( ! -p>ticle 7helium atom74 ,! collision exp]im5ts on :i* ,ru!r=d's !ory is f\nd$ are ( s direct & decisive a "* t "o c h>dly call x a !ory1 b r a fact1 f\nd$ on obs]vation1 %[+ conclusively t ! atom is built aft] ! fa%ion indicat$4 ,cont9u$ rese>*es h amass$ a quantity ( important facts ab\t atoms4 ,?us1 ,ru!r=d 0 able to %[ t ! radius ( ! nucleus is ( ! ord] ( magnitude #aj to #aj;cm4 ,?is means really t x is only :5 an -p>ticle approa*es s ne> ! c5tre ( an atom t =ces come into play :i* no long] foll[ ,c\lomb's ,law = ! repulsion betwe5 two po9t *>ges ( ! same sign 79 contra/ to ! case 9 ! ord9>y deflections ( -p>ticles74 ,x %\ld be rem>k$1 h[ev]1 t 9 ! case ( ! hydrog5 nucleus !oretical consid]ations give f\ndation = ! assumption t its radius is really _m times small] ?an ! radius ( ! electron1 :i* is "s #bjjj times light]2 exp]im5ts by :i* ?is assumption c be te/$ are n at h& at pres5t4 ,! ,nucle> ,*>ge2 ,atomic ,numb]2 ,atomic ,weight4 ,x is n necess>y to h rec\rse to a new rese>* to det]m9e ! masses ( ! nuclei ( v>i\s atoms1 because ! mass ( ! nucleus is = all practical purposes ! mass ( ! atom4 ,accord+ly1 if ! mass ( ! hydrog5 nucleus is tak5 z unity1 ! atomic mass is equal to ! atomic weight z previ\sly def9$4 ,! individual electrons :i* accompany ! nucleus are s light t _! mass has relatively little influ5ce 7)9 ! limits ( exp]im5tal accuracy7 on ! total mass ( ! atom4 ,on ! o!r h&1 a problem ( ! greate/ importance :i* imm$iately sugge/s itself is to det]m9e ! magnitude ( ! positive *>ge ( ! nucleus4 ,?is naturally mu/ be an integral multiple ( ! fundam5tal quantum ( negative electricity1 namely1 #dgg #aj electro/atic units1 or if we pref] to call ?is simply ! 8unit0 *>ge1 !n ! nucle> *>ge mu/ be an integ]4 ,o!rwise a neutral atom c\ld n be =m$ ( a nucleus & electrons1 = 9 a neutral atom ! numb] ( negative electrons :i* move ab\t ! nucleus mu/ be equal to ! numb] ( positive *>ges 9 ! nucleus4 ,! det]m9ation ( ?is numb] is1 accord+ly1 equival5t to ! settl+ ( ! important "q1 h[ _m electrons surr\nd ! nucleus 9 ! normal neutral /ate ( ! atom ( ! elem5t 9 "q4 ,! answ] to ! "q is easie/ 9 ! case ( ! helium atom4 ,= :5 ?is is expell$ z an -p>ticle1 x c>ries1 z ,ru!r=d 0 able to %[1 a positive *>ge ( two units--9 o!r words1 two electrons are necess>y to *ange ! positive ion into a neutral atom4 ,at ! same "t !re is e reason to suppose t ! -p>ticle is simply a helium nucleus depriv$ ( its electrons2 x foll[s1 !re=e1 t ! electron sy/em ( ! neutral helium atom consi/s ( two electrons4 ,s9ce ! atomic weight ( helium is f\r1 ! numb] ( electrons is consequ5tly "o-half ! atomic weight4 ,ru!r=d's inve/igation ( ! deflections ( -p>ticles 9 pass+ ?r\gh v>i\s m$ia _h already l$ him to believe t = _m o!r elem5ts1 to a consid]able approximation1 ! nucle> *>ge & h5ce ! numb] ( electrons 0 equal to half ! atomic weight4 ,hydrog51 ( c\rse1 mu/ =m an exception1 s9ce its atomic weight is unity4 ,! positive *>ge on ! hydrog5 nucleus is "o elem5t>y quantum1 & 9 ! neutral /ate ( ! atom1 only "o electron rotates ab\t x4 ,fig4 #bc gives a repres5tation ( ! /ructure ( ! hydrog5 atom1 & ! /ructures ( ! two types ( hydrog5 ions =m$ respectively by ! loss & ga9 ( an electron4 ,9 ! picture1 ! position ( ! electron is1 ( c\rse1 arbitr>y1 & = ! sake ( simplicity its pa? is suppos$ to be circul>4 ,illu/ration3 ,,fig4 #bc4--,s*ematic repres5tation ( ! nucle> atom4 ,a1 a neutral hydrog5 atom2 ,b1 a positive1 & ,c1 a negative hydrog5 ion2 ,k1 atomic nuclei2 ,e1 electrons4 ,z has j be5 indicat$1 ,ru!r=d's rule = ! numb] ( electrons is only an approximation4 ,a ,dut* physici/1 van d5 ,broek1 conceiv$ 9 ! meantime ! idea t ! numb] ( electrons 9 ! atom ( an elem5t is equal to its ord] numb] 9 ! p]iodic table 7its 8atomic numb]10 z x is n[ call$74 ,especially ?r\gh a sy/ematic inve/igation ( ! ,x-ray spectra *>act]i/ic ( ! diff]5t elem5ts ?is has prov$ to be ! correct rule4 ,9 fact1 us+ ,bragg's reflection me?od ( ,x-rays f cry/al surfaces 7cf4 p4 #ed71 ! ,engli%man1 ,moseley1 made 9 #aiad ! f>-rea*+ discov]y t ^! spectra possess an exceptionally simple /ructure1 :i* made x possible 9 a simple way to atta* an ord] numb] to ea* elem5t 7giv5 on p4 #bc74 ,on ! basis ( ,bohr's !ory1 e/abli%$ a ye> be=e1 x c\ld be directly prov$ t ?is ord] numb] mu/ be id5tical ) ! numb] ( positive elem5t>y *>ges on ! nucleus4 ,! numb] :i* =m]ly indicat$ simply ! position ( an elem5t 9 ! p]iodic sy/em has ?us obta9$ a pr(\nd physical significance1 & 9 comp>ison ! atomic weight has come to h b a second>y mean+4 ,! inv]sion ( argon & potassium 9 ! p]iodic sy/em 7m5tion$ on p4 #ba71 :i* seem$ to be an exception to ! regul>ity display$ by ! sy/em z a :ole1 obta9s an easy explanation on ! van d5 ,broek rule2 = to expla9 ! inv]sion we ne$ only assume t potassium has "o electron m ?an argon1 ?\gh its atomic weight is less ?an t ( argon4 ,we see at once t ! atomic weight & numb] ( electrons 7or :at is ! same ?+--! nucle> *>ge7 are n directly correlat$ to ea* o!r4 ,& s9ce ! p]iodic sy/em bas$ on ! atomic numb] repres5ts ! correct arrangem5t ( ! elem5ts accord+ to _! respective prop]ties 7especially _! *emical prop]ties71 we are l$ naturally to ! conclusion t x is ! atomic numb] & n ! atomic weight t det]m9es *emical *>act]i/ics4 ,! conception ( ! relatively great importance ( ! atomic numb] z comp>$ ) ! atomic weight has 9 rec5t ye>s receiv$ ov]:elm+ support f ! rese>*es ( ,soddy1 ,fajans1 ,russell1 ,hevesy & o!rs :o h discov]$ ! exi/5ce ( s-call$ isotope elem5ts 7f ! ,greek isos same1 & topos place71 sub/ances ) diff]5t nucle> masses 7atomic weights7 & diff]5t radioactive prop]ties 7if !re are any71 b ) ! same nucle> *>ge1 ! same numb] ( electrons &1 consequ5tly1 occupy+ ! same place 9 ! p]iodic sy/em4 ,two su* isotopes are practically equival5t 9 all _! *emical prop]ties z well z 9 mo/ ( _! physical *>act]i/ics4 ,"o ( ! olde/ examples ( isotopes is provid$ by ord9>y lead ) ! atomic weight #bjgb & ! sub/ance f\nd 9 pit*bl5de ) ! atomic weight #bjf1 b id5tical1 *emically1 ) ord9>y lead4 ,?is latt] =m ( lead has already be5 ref]r$ to on p4 #gi z ! end product ( radioactive dis9tegrations1 & h5ce x is sometimes call$ radium lead4 ,by 8 inve/igations ( canal rays ! ,engli% physici/ ,a/on has j rec5tly %[n t _m sub/ances :i* h always be5 assum$ to be simple elem5ts1 are 9 reality mixtures ( isotopes4 ,! atomic weight ( *lor9e det]m9$ 9 ! usual way is #cee1 b 9 ! dis*>ge tube two k9ds ( *lor9e atoms appe>1 hav+ atomic weights #ce & #cg respectively2 & x mu/ be assum$ t ^! two k9ds ( *lor9e are pres5t 9 all ! comp\nds ( *lor9e kn[n on ! e>? 9 ! ratio (1 r\ghly1 ?ree to "o4 ,to sep>ate su* mixtures into _! con/itu5t p>ts is extremely difficult1 precisely because ! con/itu5ts h id5tical prop]ties ap>t f a small diff]5ce 9 d5sity1 :i* /&s 9 direct connection ) ! atomic weight4 ,su* a sep>ation 0 fir/ c>ri$ out successfully by ! ,dani% *emi/1 ,brn/$1 9 collaboration ) ! ,hung>ian *emi/1 ,hevesy 7#aiba74 ,^! two sci5ti/s 7 able to sep>ate a l>ge quantity ( m]cury ( d5sity #aceiee into two portions ( slightly diff]5t d5sities4 ,all ! diff]5t isotopes ( :i* m]cury is a mixture 71 inde$1 n :olly sep>at$2 !y 7 repres5t$ 9 ! two portions 9 diff]5t proportions4 ,?us1 9 "o ( ! fir/ attempts1 ! d5sity ( ! "o "p 0 #aceihf & ( ! o!r #aceibj 7at #j ,c74 ,x is a p]fectly reasonable supposition t x is ! electron sy/em :i* det]m9es ! ext]nal prop]ties ( ! atom1 t is1 ^? prop]ties :i* dep5d on ! int]play ( two or m atoms4 ,= ! electron1 rotat+ ab\t ! nucleus at a consid]able di/ance1 sep>ates1 s to speak1 ! nucleus f ! surr\nd+ space1 & mu/ !re=e be assum$ to be ! organ :i* connects ! atom ) ! re/ ( ! univ]se4 ,"o might also expect ! /ructure ( ! electron sy/em to dep5d :olly on ! nucle> *>ge1 i4e4 on ! atomic numb] & n on ! mass ( ! nucleus1 s9ce x is ! nucle> electrical attraction :i* holds ! electrons 9 _! orbits & n ! relatively insignificant gravitational attraction4 ,x ?us becomes intelligible t ! prop]ties ( ! elem5ts c be divid$ into two %>ply def9$ classes1 namely3 7#a7 prop]ties ( ! nucleus1 & 7#b7 prop]ties ( ! electron sy/em 9 ! atom4 ,! cr$it = fir/ recogniz+ ! %>p di/9ction betwe5 ^! two classes1 a di/9ction fundam5tal = a detail$ /udy ( ! atom1 is due to ,niels ,bohr4 ,! prop]ties ( ! nucleus det]m9e--7a7 ! radioactive processes1 or explosions ( ! nucleus1 & relat$ processes2 7b7 collisions1 :]e two nuclei approa* extremely ne> to ea* o!r2 & 7c7 weight :i*1 z m5tion$ above1 /&s 9 direct connection ) atomic weight4 ,! prop]ties ( ! electron sy/em are1 on ! o!r h&1 ! det]m9+ factors 9 all o!r physical & *emical activities1 &1 z has be5 /at$1 are functions1 we may say1 ( ! atomic numb] ( ! giv5 elem5t4 ,! ,bohr !ory may be said to conc]n itself ) ! *emical & physical prop]ties ( ! atom ) ! exception ( ^? :i* h to d ) ! nucleus4 ,we %all consequ5tly devote our att5tion 9 ! next *apt]s to ! electron sy/em4 ,b be=e turn+ to ?is we %all dwell a little fur!r ^u ! atomic nucleus4 ,! ,/ructure ( ! ,nucleus4 ,t ! nucleus is n an elem5t>y indivisible p>ticle b a sy/em ( p>ticles1 is cle>ly %[n by ! radioactive processes 9 :i* -p>ticles & -p>ticles 7electrons7 are %ot out ( ! nuclei ( radioactive elem5ts4 ,bohr 0 ! fir/ to see cle>ly t n only ! -p>ticles emitt$ 9 su* cases come f ! nucleus1 b t ! -p>ticles also h _! s\rce !re4 ,!re is n[ no d\bt t1 9 addition to ! out] electrons ( ! atom1 :i* are ! det]m9+ factor 9 ! atomic numb]1 !re mu/ also be1 9 ! radioactive sub/ances at any rate1 special nucle> electrons :i* lead a m hidd5 exi/5ce 9 ! int]ior ( ! nucleus4 ,"o c easily und]/& t isotopes may result z products ( radioactive dis9tegration4 ,= example1 let u suppose t a nucleus emits fir/ an -p>ticle 7i4e4 a helium nucleus ) two positive *>ges71 & !reaft] s5ds out two electrons1 ea* ) its negative *>ge1 9 two new dis9tegrations4 ,! nucle> *>ge 9 ! resultant atom w !n obvi\sly be ! same z be=e1 because ! loss ( ! two electrons exactly neutralizes t ( ! -p>ticle4 ,b ! atomic weight w be dim9i%$ by f\r units 7i4e4 ! weight ( ! helium nucleus1 rememb]+ also t ! electrons h b v negligible masses74 ,among ! radioactive sub/ances are recogniz$ _m examples ( isotope elem5ts1 ) atomic weights diff]+ precisely by f\r4 ,! radioactive elem5t uranium is ! elem5t ) ! greate/ atomic weight 7#bch71 & atomic numb] 7#ib71 & consequ5tly ) ! greate/ nucle> *>ge4 ,almo/ all ! o!r radioactive sub/ances are ^? ) high atomic numb]s 9 ! p]iodic sy/em4 ,! cause ( radioactivity mu/ be s\ght 9 ! hypo!sis t ! nuclei ( ! radioactive elem5ts are v complicat$ sy/ems ) small /ability1 & !re=e break d[n r easily into less complicat$ & m /able sy/ems ) ! emission ( "s ( _! con/itu5t p>ticles2 ! corpuscul> rays ?us produc$ possess a consid]able am\nt ( k9etic en]gy4 ,accord+ly1 by analogy1 ! nuclei ( ! non-radioactive elem5ts may be assum$ to be compos$ ( nucle> electrons & positive p>ticles2 hydrog5 alone except$4 ,! simple/ assumption is t ! hydrog5 nucleus is ! real quantum or atom ( positive electricity1 j z ! electron is ! atom ( negative electricity4 ,on ?is !ory all sub/ances are built up ( two k9ds only ( fundam5tal p>ticles1 namely1 hydrog5 nuclei & electrons4 ,t ^! p>ticles may !mselves consi/ ( con/itu5t p>ts is1 ( c\rse1 an op5 possibility1 b su* speculation is beyond our exp]i5ce up to ! pres5t4 ,9 e nucleus !re are m positive hydrog5 nuclei ?an !re are negative electrons1 s t ! nucleus has a residual positive *>ge ( a magnitude equal to ! diff]5ce betwe5 ! numb] ( hydrog5 nuclei & nucle> electrons4 ,if we n[ pass f hydrog5 :i* has ! atomic weight1 atomic numb] & nucle> *>ge ( unity1 we next enc\nt] helium ) ! atomic weight #d1 atomic numb] & nucle> *>ge #b4 ,! helium nucleus %\ld !re=e consi/ ( #d hydrog5 nuclei1 :i* w\ld toge!r acc\nt = ! atomic weight ( #d4 ,b s9ce ^! repres5t #d positive *>ges1 !re mu/ also be pres5t 9 ! nucleus #b negative electrons to make ! resultant nucle> *>ge equal to #b4 ,we c\ld inde$ h>dly conceive ( a sy/em compos$ ( #d positive hydrog5 nuclei alone2 = ! =ces ( repulsion w\ld soon drive ! sep>ate p>ts asund]4 ,! two electrons c1 s to speak1 s]ve to hold ! sy/em toge!r4 ,fig4 #bd gives a r\gh repres5tation ( ! helium atom4 ,x mu/ be c>efully not$ t ! picture is purely s*ematic & ! di/ances arbitr>y4 ,! helium nucleus1 compos$ ( #d hydrog5 nuclei & #b electrons1 seems to possess extreme /ability1 & x is n improbable t helium nuclei occur z high] units 9 ! /ructure ( ! nuclei ( n only ! radioactive sub/ances b also ! o!r elem5ts4 ,we %all p]haps be v ne> ! tru? 9 say+ t all nuclei are built up ( comb9ations ( hydrog5 nuclei1 helium nuclei & electrons4 ,illu/ration3 ,,fig4 #bd4--,s*ematic repres5tation ( a helium atom4 ,k1 nucle> sy/em ) f\r hydrog5 nuclei & two nucle> electrons2 ,e1 electrons 9 ! out] electron sy/em4 ,9 nitrog51 ) ! atomic weight #ad & atomic numb] #g1 ! nucleus %\ld consi/ ( #ad hydrog5 nuclei 7) #ab ( !m comp\nd$1 p]haps1 into #c helium nuclei7 & #g nucle> electrons1 r$uc+ ! resultant positive nucle> *>ge f #ad to #g4 ,uranium1 ) atomic numb] #ib & atomic weight #bch1 %\ld h a nucleus compos$ ( #bch hydrog5 nuclei & #adf electrons1 & s on = ! o!rs4 ,we see at once t ! conception ( ! nucleus "h prop\nd$ leads u back to ! old hypo!sis ( ,pr\t 7see p4 #ae7 t all atomic weights %\ld be integral multiples ( t ( hydrog54 ,?is hypo!sis app>5tly disagre$ ) atomic weight measurem5ts1 b ! isotope rese>*es h vanqui%$ ?is difficulty2 ?us x has be5 m5tion$ be=e t *lor9e ) an atomic weight ( #cee appe>s to be a mixture ( isotopes ) atomic weights #ce & #cg1 & o!r cases h a simil> explanation4 ,yet ! rule _c be :olly & completely exact4 ,=1 9 ! fir/ place1 ! mass ( ! electrons mu/ contribute some?+1 ?\gh ?is contribution is f> too small to be measur$4 ,b !re is also a second matt] :i* plays a "p "h4 ,?is is ! law enunciat$ by ,e9/e9 9 8 relativity !ory1 t e increase or decrease 9 ! en]gy ( a body is correlat$ ) an increase or decrease 9 ! mass ( ! body1 proportional to ! en]gy *ange4 ,we mu/1 !re=e1 expect t ! masses ( ! v>i\s atomic nuclei w dep5d n only on ! numb] ( hydrog5 nuclei 7& electrons71 b also on ! en]gy repres5t$ 9 ! attractions & repulsions betwe5 ! p>ticles ( ! sy/em1 & 9 _! mutual motions1 or ! en]gy :i* comes into play 9 ! =mation & dis9tegration ( nucle> sy/ems4 ,?is is presumably closely connect$1 al?\gh 9 a way :i* is n cle>ly und]/ood1 ) ! fact1 t if ! atomic weights ( ! elem5ts are to come out integ]s1 t ( hydrog5 mu/ n be tak5 z #a b z #ajjh2 t is1 ! atomic weight unit mu/ be *os5 a little small] ?an ! atomic weight ( hydrog5 7cf4 table1 p4 #bc74 ,trans=mation ( ,elem5ts & ,lib]ation ( ,atomic ,en]gy4 ,we %all n[ treat v briefly two que/ions :i* h pr(\ndly int]e/$ _m p1 because !y are conc]n$ ) possible practical applications ( our new k ( atoms4 ,! fir/ "q is ?is3 ,c "o n1 f ?is k1 br+ ab\t ! trans=mation ( "o elem5t into ano!r8 ,9 answ]+ ?is1 x c1 ( c\rse1 be said imm$iately t among ! radioactive sub/ances su* trans=mations are con/antly tak+ place )\t human int]f]5ce1 & we c]ta9ly h no "r to /ate (fh& t x w be impossible = man ev] to br+ ab\t su* a trans=mation artificially4 ,= example1 if we c\ld succe$ 9 gett+ "o hydrog5 nucleus loose f ! nucleus ( m]cury1 ! latt] w\ld !reby be *ang$ into a gold nucleus4 ,su* a ?+ is n only conceivable1 b 9 ! la/ few ye>s x has become a reality1 ?\gh1 to be sure1 n ) ! sub/ances "h m5tion$4 ,9 #aiai ,ru!r=d1 by bomb>d+ nitrog5 7,n #ad7 ) -p>ticles1 0 able to knock loose "s hydrog5 nuclei f ! nitrog5 nucleus2 p]haps he succe$$ !reby 9 *ang+ ! nitrog5 nuclei into c>bon nuclei 7,c #ab7 by ! break+ (f ( two hydrog5 nuclei f ea* nitrog5 nucleus4 ,b to dis9tegrate v few nitrog5 nuclei1 ,ru!r=d _h to employ a =midable bomb>dm5t ) hundr$s ( ?\s&s ( projectiles 7-p>ticles72 & ev5 if he _h end$ ) gold in/ead ( c>bon1 ?is w\ld h be51 f ! economic po9t ( view1 a v fooli% way ( mak+ gold2 & at ! pres5t "t we "k ( no o!r artificial me?od = ! trans=mation ( elem5ts4 ,t ,ru!r=d's inve/igation has1 9 any case1 extraord9>ily great int]e/ & sci5tific value is ano!r matt]4 ,! second "q is :e!r "o _c lib]ate & utilize ! en]gy lat5t 9 ! int]ior ( ! atom4 ,?is "q1 :i* 0 sugge/$ 9 ! fir/ in/ance by ! discov]y ( radium1 has rec5tly attract$ consid]able att5tion because ( reports t1 accord+ to ,e9/e9's relativity !ory1 "o gram ( any sub/ance by virtue ( its mass alone mu/ conta9 a quantity ( en]gy equal to t produc$ by ! burn+ ( #cjjj tons ( coal4 ,! mean+ ( ?is /atem5t is ?is3 x has already be5 m5tion$ t accord+ to ! relativity !ory a decrease 9 ! en]gy ( a body br+s ab\t a decrease 9 its mass2 x is immat]ial 9 :at =m ! en]gy is giv5 up1 :e!r z heat1 ela/ic oscillations1 or ! l2 all t is said is1 t to a c]ta9 decrease 9 mass1 w correspond a p]fectly def9ite emission ( en]gy 9 "s =m4 ,if we n[ c\ld imag9e ! :ole mass ( "o gram ( a sub/ance to be 8de/roy$0 7i4e4 caus$ to disappe> utt]ly z a physical sub/ance71 & to reappe> z heat en]gy1 = example1 !n we c\ld compute f ! kn[n relation betwe5 mass & en]gy1 t ! heat en]gy ?us br\ght ab\t w\ld be equival5t to t obta9$ by ! burn+ ( #cjjj tons ( coal4 ,b 9 ord] t all ?is en]gy %\ld be develop$1 ev5 ! hydrog5 nuclei & ! electrons w\ld h to be 8de/roy$10 & no ph5om5on is kn[n1 support+ ! supposition t su* a 8de/ruction0 ( ! fundam5tal p>ticles ( a sub/ance is possible1 or t x is possible to trans=m ^! p>ticles into o!r types ( en]gy4 ,a ?\ght l ?is mu/ r be /amp$ z fantasy1 ! orig9 ( :i* is to be f\nd 9 a misund]/&+ ( a purely sci5tific mode ( expression4 ,! case is ess5tially diff]5t ) ^? quantities ( en]gy :i* mu/ be assum$ to be fre$ or absorb$ 9 ! trans=mation ( "o nucle> sy/em into ano!r1 t is1 9 elem5tal trans=mations4 ,?\gh ^! are f> small] 9 am\nt1 ! radioactive processes indicate t !y are n :olly to be despis$4 ,= "o gram ( radium w ^u complete dis9tegration to non-radioactive mat]ial give (f z mu* en]gy z is equival5t to #dfj kg4 ( coal4 ,b ev5 "h we mu/ confess t x w take ab\t #agjj ye>s = only half ( ! radium to be trans=m$4 ,x is n at all impossible t o!r elem5tal trans=mations might lead to j z great en]gy developm5ts z appe> 9 ! dis9tegration ( radioactive sub/ances4 ,let u imag9e t f\r hydrog5 nuclei1 :i* toge!r h a mass ( #d #ajjh #djcb1 & two electrons c\ld jo9 toge!r to =m a helium nucleus ) atomic weight v close to #d4 ,?is process w\ld ?us result 9 a loss ( mass :i* mu/ be assum$ to appe> 9 ano!r =m ( en]gy4 ,! am\nt ( en]gy obta9able 9 ?is way f "o gram ( hydrog5 w\ld be consid]ably m ?an t giv5 (f by ! dis9tegration ( "o gram ( radium4 ,!re c h>dly exi/ any d\bt t 9 nature !re occur n only dis9tegrations1 b also 7p]haps 9 ! int]ior ( ! />s7 build+-up processes 9 :i* comp\nd nuclei result f simple ones4 ,x is !re=e natural to suppose t by ex]t+ on hydrog5 exceptional conditions ( temp]ature1 pressure1 electrical *anges1 etc41 we c\ld succe$ by exp]im5ts "h on e>? 9 =m+ helium f x ) ! developm5t ( consid]able en]gy4 ,b at ! same "t x is v likely t ev5 "u fav\rable circum/ances su* a process w\ld take place ) v great sl[ness1 because ! =mation ( a helium nucleus might well be a v infrequ5t occurr5ce2 x w\ld probably be ! result ( a c]ta9 succession ( collisions betwe5 hydrog5 nuclei & electrons1 a comb9ation ^: probability ( occurr5ce 9 a c]ta9 numb] ( collisions is inf9itely less ?an ! probability ( w9n+ ! l>ge/ prize 9 a lott]y ) ! same numb] ( *ances4 ,nature has "t en\gh to wait = 8w9s10 :ile mank9d un=tunately has n4 ,we "k conc]n+ ! dis9tegration ( ! radioactive sub/ances t x is ( ! "* "h indicat$2 ( ! great numb] ( atoms to be f\nd 9 a v small mass ( a radioactive sub/ance1 n[ "o explodes & n[ ano!r4 ,b :y =tune %\ld pick out "o p>ticul> atom is z difficult to und]/& z :y 9 a lott]y "o p>ticul> numb] %\ld prove to be ! lucky "o r ?an any o!r4 ,our only und]/&+ ( ! :ole matt] re/s on ! law ( av]ages1 or probability z we may call x4 ,we "k t ( a billion radium atoms 7#aj7 on ! av]age ?irte5 explode e second2 & ev5 if 9 any s+le collection ( a billion a few m or a few less may explode1 ! av]age ( ?irte5 p] second p] billion w always be ma9ta9$ 9 deal+ ) l>g] & l>g] numb]s ( atoms1 z1 = example1 ) a ?\s& billion or a million billion4 ,= o!r radioactive sub/ances we get :olly diff]5t av]ages = ! numb] ( atoms dis9tegrat+ p] second2 b 9 no case are we able to p5etrate into ! inn] "* ( ! process ( dis9tegration itself4 ,& :at holds true ( ! radioactive sub/ances w also hold true probably = elem5tal *anges ( all k9ds2 ,ru!r=d ) 8 hundr$s ( ?\s&s ( -p>ticle projectiles 0 able to make sure ( b a few lucky 8%ots40 ,! :ole matt] mu/ at ?is /age be look$ ^u z gov]n$ :olly by *ance4 ,"o int]e/$ 9 speculat+ on :at w\ld happ5 if x 7 possible to br+ ab\t artificially a trans=mation ( elem5ts propagat+ itself f atom to atom ) ! lib]ation ( en]gy1 w\ld f9d food = s]i\s ?\ght 9 ! fact t ! quantities ( en]gy :i* w\ld be lib]at$ 9 ?is way w\ld be _m1 _m times great] ?an ^? :i* we n[ "k ( 9 connection ) *emical processes4 ,!re is !n (f]$ ! possibility ( explosions m ext5sive & m viol5t ?an any :i* ! m9d c n[ conceive4 ,! idea has be5 sugge/$ t ! _w cata/rophes repres5t$ 9 ! heav5s by ! sudd5 appe>ance ( v bright />s may be ! result ( su* a release ( sub-atomic en]gy1 br\ght ab\t p]haps by ! 8sup]-wisdom0 ( ! unlucky inhabitants !mselves4 ,b ?is is1 ( c\rse1 m]e fanciful conjecture4 ,x seems cle>1 h[ev]1 t we ne$ h no fe> t 9 inve/igat+ ! problem ( atomic en]gy we are releas+ =ces :i* we _c control1 because we c at pres5t see no way to lib]ate ! en]gy ( atomic nuclei beyond t :i* ,nature h]self provides1 to say no?+ ( a practical solution ( ! en]gy problem4 ,! "t has c]ta9ly n yet come = ! te*nician to foll[ 9 ! !oretical inve/igator's foot/eps 9 ?is bran* ( sci5ce4 ,"o hesitates1 h[ev]1 to pr$ict :at ! future may br+ =?4 ,int]e/+ & significant z is ! insight :i* ,ru!r=d & o!rs h op5$ up into ! inn] work+s ( ! nucleus1 ! /udy ( ! electron sy/em ( ! atom be>s m intimately ^u ! v>i\s bran*es ( physical & *emical sci5ce1 & h5ce pres5ts great] possibilities ( atta9+1 9 a less remote future1 to discov]ies ( practical significance4 ,,*apt] ,v ,,! ,,bohr ,,!ory ,,( ,,! ,,hydrog5 ,,spectrum ,! ,nucle> ,atom & ,electrodynamics4 ,ev5 if ,ru!r=d _h n yet succe$$ 9 giv+ a complete answ] to ! fir/ ( ! que/ions prop\nd$ 9 ! previ\s *apt]1 namely1 t conc]n+ ! positions ( ! positive & negative p>ticles ( ! atom1 "o might at any rate hope t 8 g5]al explanation ( ! /ructure ( ! atom--t is1 ! division into ! nucleus & surr\nd+ electrons1 & ! det]m9ation ( ! numb] ( electrons 9 ! atoms ( ! v>i\s elem5ts--w\ld furni% a good f\ndation = ! answ] to ! second "q ab\t ! connection betwe5 ! atomic processes & ! physical & *emical prop]ties ( matt]4 ,b 9 ! beg9n+ ?is seem$ s f> f be+ true t x appe>$ almo/ hopeless to f9d a solution ( ! problem ( ! atom 9 ?is way4 ,we %all be/ und]/& ! mean+ ( ?is if we consid] ! simple/ ( ! elem5tal atoms1 namely1 ! atom ( hydrog5 ) its positive nucleus & its "o electron revolv+ ab\t ! nucleus4 ,h[ c\ld x be possible to expla9 f su* a simple /ructure ! _m %>p spectral l9es giv5 by ! ,balm]-,ritz =mula 7p4 #eg78 ,z has previ\sly be5 m5tion$1 ! classical electron !ory seem$ to dem& a v complicat$ atomic /ructure = ! explanation ( ^! l9es4 ,accord+ to ! electron !ory1 ! atoms may be lik5$ to /r+$ in/rum5ts :i* are capable ( emitt+ a great numb] ( tones1 & 9 ^! atoms ! electrons are naturally suppos$ to correspond to ! 8/r+s40 ,b ! hydrog5 atom has only "o electron1 & x h>dly seems cr$ible t 9 a mass ( hydrog5 ! individual atoms w\ld be tun$ = diff]5t 8tones10 ) def9ite frequ5cies ( vibration4 ,n[1 x c]ta9ly _c be conclud$ f ! analogy ) ! /r+$ in/rum5t t a s+le electron c emit light ( only a s+le frequ5cy at "o "t1 correspond+ to a s+le spectral l9e4 ,= a pluck$ /r+ w1 z we "k1 give rise to a simple tone only if x vibrates 9 a v def9ite & p>ticul>ly simple way2 9 g5]al x w emit a comp\nd s\nd :i* may be conceiv$ z made up ( a 8fundam5tal0 & its s-call$ 8ov]tones10 or 8h>monies0 ^: frequ5cies are #b1 #c1 444 times t ( ! fundam5tal 7i4e4 integral multiples ( ! latt]74 ,^! ov]tones may arise ev5 sep>ately because ! /r+1 in/ead ( vibrat+ z a :ole1 may be divid$ into #b1 #c1 444 equally long vibrat+ p>ts1 giv+ respectively #b1 #c1 444 times z great frequ5cies ( vibration4 ,we call su* vibrations 8h>monic oscillations40 ,! simultane\s exi/5ce ( ^! diff]5t modes ( oscillation ( ! /r+ may be ?\ght ( 9 ! same way z ! simultane\s exi/5ce ( wave sy/ems ( diff]5t wave-l5g?s on ! surface ( wat]4 ,correspond+ to ! possibility ( resolv+ ! motion ( ! /r+ into its 8h>monic compon5ts10 ! comp\nd s\nd waves produc$ by ! /r+ c be resolv$ by resonators 7cf4 p4 #dd7 into tones possess+ ! frequ5cies ( ^! compon5ts4 ,accord+ to ! laws ( electrodynamics ! situation ) ! electron revolv+ ab\t ! hydrog5 nucleus might be expect$ to be some:at simil> to t describ$ above 9 connection ) ! vibrat+ /r+4 ,if ! orbit ( ! electron 7 a circle1 x %\ld emit into ! e!r electromagnetic waves ( a s+le def9ite wave-l5g? & correspond+ frequ5cy1 1 equal to 1 ! frequ5cy ( rotation ( ! electron 9 its orbit2 t is1 ! numb] ( revolutions p] second4 ,b j z a planet "u ! attraction ( ! sun1 v>y+ inv]sely z ! squ>e ( ! di/ance1 moves 9 an ellipse ) ! sun at "o focus1 s ! electron1 "u ! attraction ( ! positive nucleus1 :i* also foll[s ! inv]se squ>e law1 w 9 g5]al be able to move 9 an ellipse ) ! nucleus at "o focus4 ,! electromagnetic waves :i* are emitt$ f su* a mov+ electron may on ! electron !ory be consid]$ z compos$ ( light waves correspond+ to a s]ies ( h>monic oscillations ) ! frequ5cies3 1 #b1 #c 444 & s on1 :]e 1 z be=e1 is ! frequ5cy ( revolution ( ! electron4 ,accord+ z ! actual orbit deviates m or less f a circle1 ! frequ5cies 1 444 w appe> /rong] or weak] 9 ! comp\nd light waves emitt$4 ,b ! actual di/ribution ( spectral l9es 9 ! real hydrog5 spectrum pres5ts no lik5ess :atev] to ?is di/ribution ( frequ5cies4 ,f ?is x is evid5t t no agreem5t c be rea*$ betwe5 ! classical electron !ory on ! "o h& & ! ,ru!r=d atom model on ! o!r4 ,inde$1 ! disagreem5t betwe5 ! two is really f> m fundam5tal ?an has j be5 indicat$4 ,accord+ to ,lor5tz's explanation ( ! emission ( light waves1 ! electrons 9 a sub/ance 7see aga9 p4 #ge7 %\ld h c]ta9 equilibrium positions1 & %\ld oscillate ab\t ^! :5 pu%$ out ( !m by "s ext]nal impulse4 ,! en]gy :i* is giv5 to ! electron by su* an impulse is exp5d$ 9 ! emission ( ! light waves & is ?us trans=m$ into radiation en]gy 9 ! emitt$ light1 :ile ! electrons fall to re/ aga9 unless !y receive 9 ! meantime a new impulse4 ,we c get an und]/&+ ( :at ^! impulses 9 v>i\s cases may be by ?9k+ ( !m1 9 ! case ( a gl[+ solid1 = example1 z due to ! collisions ( ! molecules2 or 9 ! case ( ! gl[+ gas 9 a dis*>ge tube1 f ! collisions ( electrons & ions4 ,! oscillat+ sy/em repres5t$ by ! electron 7! 8oscillator07 w possess "u ^! circum/ances great analogy ) a /r+ :i* aft] be+ set into vibration by a /roke gradually comes back to re/1 :ile ! en]gy exp5d$ 9 ! /roke is emitt$ 9 ! =m ( s\nd waves4 ,al?\gh ! vibrations ( ! /r+ become weak] aft] a :ile1 ! p]iod ( ! vibrations w rema9 un*ang$2 ! /r+ vibrations l p5dulum oscillations h an inv>iable p]iod1 & ! same w be ! case ) ! frequ5cy ( ! electron if ! =ce :i* pulls x back into its equilibrium position is directly proportional to ! displacem5t f ?is position 7! 8h>monic motion0 =ce74 ,ru!r=d's atomic model is1 h[ev]1 a sy/em ( a k9d :olly diff]5t f ! 8oscillator0 ( ! electron !ory4 ,! "o revolv+ hydrog5 electron w f9d a position ( 8re/0 or equilibrium only 9 ! nucleus itself1 & if x once becomes unit$ ) ! latt] x w n easily escape2 x w !n probably become a nucle> electron1 & su* a process w\ld be no?+ less ?an a trans=mation ( elem5ts 7see p4 #gi74 ,on ! o!r h&1 x foll[s necess>ily f ! fundam5tal laws ( electrodynamics t ! revolv+ electron mu/ emit radiation en]gy1 &1 because ( ! resultant loss ( en]gy1 mu/ gradually %r9k its pa? & approa* ne>] ! nucleus4 ,b s9ce ! nucle> attraction on ! electron is inv]sely proportional to ! squ>e ( ! di/ance1 ! p]iod ( revolution w be gradually decreas$ & h5ce ! frequ5cy ( revolution 1 & ! frequ5cy ( ! emitt$ light w gradually increase4 ,! spectral l9es emitt$ f a great numb] ( atoms %\ld1 accord+ly1 be di/ribut$ ev5ly f ! r$ end ( ! spectrum to ! violet1 or 9 o!r words !re %\ld be no l9e spectrum at all4 ,x is ?us cle> t ,ru!r=d's model 0 n only unable to acc\nt = ! numb] & di/ribution ( ! spectral l9es2 b t ) ! application ( ! ord9>y electrodynamic laws x 0 q impossible to acc\nt = ! exi/5ce ev5 ( spectral l9es4 ,inde$1 x _h to be admitt$ t an electrodynamic sy/em ( ! k9d indicat$ 0 me*anically un/able & !re=e an impossible sy/em2 & ?is w\ld apply n m]ely to ! hydrog5 atom1 b to all nucle> atoms ) positive nuclei & sy/ems ( revolv+ electrons4 ,h[ev] "o looks at ! matt]1 !re ?us appe>s to be an irrem$iable disagreem5t betwe5 ! ,ru!r=d !ory ( atomic /ructure & ! fundam5tal electrodynamic assumptions ( ,lor5tz's !ory ( electrons4 ,z has be5 emphasiz$1 h[ev]1 ,ru!r=d f\nd$ 8 atomic model on su* a direct & cle>-cut inve/igation t any o!r int]pretation ( 8 exp]im5ts is h>dly possible4 ,if ! result to :i* he atta9$ c\ld n be reconcil$ ) ! !ory ( electrodynamics1 !n1 z has be5 said1 ?is 0 s mu* ! worse = ! !ory4 ,x c\ld1 h[ev]1 h>dly be expect$ t physici/s 9 g5]al w\ld be v will+ to give up ! conceptions ( electrodynamics1 ev5 if its basis 0 be+ s]i\sly damag$ by ,ru!r=d's atomic projectiles4 ,surm\nt$ by its cr[n+ glory--! ,lor5tz electron !ory--! classical electrodynamics /ood at ! beg9n+ ( ! pres5t c5tury a /ructure bo? solid & spaci\s1 unit+ 9 its con/ruction ne>ly all ! physical k accumulat$ dur+ ! c5turies1 optics z well z electricity1 !rmodynamics z well z me*anics4 ,) ! collapse ( su* a /ructure "o might well feel t physics _h sudd5ly become homeless4 ,! ,quantum ,!ory4 ,9 a field completely diff]5t f ! above ! conclusion _h also be5 rea*$ t !re 0 some?+ wrong ) ! classical electrodynamics4 ,?r\gh 8 v ext5d$ speculations on !rmodynamic equilibrium 9 ! radiation process1 ,planck 7#aijj7 _h rea*$ ! po9t ( view express$ 9 8 quantum !ory1 :i* 0 j z irreconcilable ) ! fundam5tal electrodynamic laws z ! ,ru!r=d atom4 ,a complete repres5tation ( ?is !ory w\ld lead u too f>2 we %all m]ely give a %ort acc\nt ( ! f\ndations on :i* x re/s4 ,by a black body is g5]ally und]/ood a body :i* absorbs all ! light fall+ ^u x1 &1 accord+ly1 c reflect none4 ,physici/s1 h[ev]1 d5ote by ! t]m 8p]fect black body0 9 an ext5d$ s5se1 a body :i* at all temp]atures absorbs all ! radiation fall+ ^u x1 :e!r ?is be 9 ! =m ( visible light1 or ultra-violet1 or infra-r$ radiation4 ,f consid]ations :i* 7 develop$ "s sixty ye>s ago by ,kir*h(f1 x c be /at$ t ! radiation :i* is emitt$ by su* a body :5 heat$ does n dep5d on ! nature ( ! body b m]ely on its temp]ature1 & t x is great] ?an t emitt$ by any o!r body :atev] at ! same temp]ature4 ,su* radiation is call$ temp]ature radiation or sometimes 8black0 radiation1 ?\gh ! latt] t]m is apt to be mislead+1 s9ce a 8p]fect black body0 emitt+ black radiation may gl[ at :ite heat4 ,x may be ( int]e/ to note "h ! fundam5tal law d$uc$ by ,kir*h(f1 :i* may be/ be illu/rat$ by say+ t good absorb]s ( radiation are also good radiators4 ,an in/ructive exp]im5t illu/rat+ ?is is p]=m$ by pa9t+ a figure 9 lampblack on a piece ( :ite porcela94 ,! lampblack surface is cle>ly a bett] absorb] ( radiant en]gy ?an ! :ite porcela94 ,:5 ! :ole is heat$ 9 a bla/ flame1 ! lampblack figure gl[s mu* m brightly ?an ! surr\nd+ porcela91 ?us %[+ t at ! same temp]ature x is also ! bett] radiator4 ,foll[+ ! same law we conclude t highly reflect+ bodies are n good radiators1 a fact t has practical significance 9 h\se heat+4 ,! p]fect black body1 !n1 be+ ! be/ absorb] ( radiation1 is also ! be/ radiator4 ,9 actual practice no body is absolutely black4 ,ev5 a body coat$ ) lampblack reflects ab\t #aj p] c5t4 ( ! light waves incid5t on x4 ,! ,dani% physici/ ,*ri/ians5 rem>k$ long ago t a real black body c\ld be produc$ only if an arrangem5t c\ld be made :]eby ! incid5t waves c\ld be reflect$ sev]al times 9 succession be=e f9ally be+ emitt$4 ,to take ! case ( lampblack1 ?ree su* reflections w\ld r$uce ! re-emission f ! lampblack$ body to only _/ ( ! radiation initially fall+ on x4 ,?is type ( black body 0 f9ally realiz$ by mak+ a cavity 9 an ov5 hav+ z its only op5+ a v small peep-hole1 & keep+ ! temp]ature ( ! wall ( ! ov5 uni=m4 ,if a ray is s5t into ! cavity ?r\gh ! peep-hole1 x w become1 s to speak1 captur$1 because1 :5 once inside x w suff] c\ntless reflections f ! walls ( ! cavity1 hav+ m & m ( its en]gy absorb$ at ea* reflection4 ,v little ( ! radiation ?us ent]+ w ev] get out aga91 & consequ5tly su* a body w act v mu* l a 8p]fect black body0 accord+ to ! !oretical def9ition above4 ,accord+ly1 ! radiation :i* is emitt$ f su* a gl[+ cavity ?r\gh ! peep-hole w be black or practically black radiation4 ,! cavity itself w be criss-cross$ 9 all directions by radiation emitt$ f "o "p ( ! inn] surface ( ! cavity & absorb$ by 7& p>tially reflect$ f7 o!r p>ts ( ! surface4 ,:5 ! walls ( ! cavity are kept at a fix$ & uni=m temp]ature !re w automatically be produc$ a /ate ( equilibrium 9 :i* e cubic c5timetre ( ! cavity w conta9 a def9ite quantity ( radiation en]gy1 dep5d5t only on ! temp]ature ( ! walls4 ,fur!r1 9 ! equilibrium /ate ! radiation en]gy w be di/ribut$ 9 a p]fectly def9ite way 7dep5d5t z be=e on ! temp]ature only7 among ! v>i\s types ( radiation correspond+ to diff]5t wave-l5g?s & frequ5cies4 ,if !re is too mu* radiation ( "o k9d & too little ( ano!r1 ! walls ( ! cavity w absorb m ( ! fir/ k9d ?an !y emit1 & emit m ( ! second k9d ?an !y absorb1 & s ! /ate w v>y until ! "r proportion = equilibrium is atta9$4 ,?is di/ribution ( ! radiation ov] widely diff]+ wave-l5g?s c be inve/igat$ by exam9+ spectroscopically ! light emitt$ f ! peep-hole 9 ! cavity4 ,!n1 by means ( a bolomet] or "s o!r in/rum5t1 ! heat developm5t 9 ! diff]5t portions ( ! spectrum c be measur$4 ,at a temp]ature ( #aejj ,c41 = example1 "o w f9d t ! maximum en]gy is repres5t$ = rays ( wave-l5g? 9 ! close vic9ity ( #ah 1 i4e4 9 ! extreme infra-r$4 ,if ! temp]ature is rais$1 ! en]gy maximum travels (f 9 ! direction ( ! violet end ( ! spectrum2 if ! temp]ature is l[]$1 x w move f>!r d[n into ! infra-r$4 ,x is also possible to make a !oretical calculation ( ! di/ribution ( en]gy 9 ! spectrum ( ! black-body radiation at a giv5 temp]ature4 ,b ! results obta9$ d n agree ) exp]im5t4 ,! ,engli% physici/s1 ,rayleigh & ,jeans1 develop$ on ! basis ( ! classical electrodynamic laws & by app>5tly conv9c+ argum5ts a di/ribution law accord+ to :i* actual radiation equilibrium becomes impossible1 s9ce if x 7 true ! en]gy 9 ! radiation w\ld t5d m & m to g ov] to ! region ( %ort wave-l5g?s & high frequ5cies1 & ?is %ift+ w\ld app>5tly g on indef9itely4 ,! !ory ?us leads to results :i* are n only 9 disagreem5t ) exp]im5t1 b :i* mu/ be look$ ^u z extremely unreasonable 9 !mselves4 ,planck1 h[ev]1 _h vanqui%$ ^! difficulties & _h obta9$ a radiation law 9 agreem5t ) exp]im5t by introduc+ an extremely curi\s hypo!sis4 ,l ,lor5tz1 he ?\ght ( radiation z produc$ ?r\gh ! m$ium ( small vibrat+ sy/ems or oscillators1 :i* c\ld emit or absorb rays ( a def9ite frequ5cy 4 ,b :ile1 accord+ to ! ,lor5tz !ory & ! classical electrodynamics1 radiation c be emitt$ 9 inf9itely small quantities 7i4e4 small )\t limit71 ,planck assum$ t an oscillator c emit & absorb en]gy only 9 c]ta9 def9ite quantities call$ quanta1 :]e ! fundam5tal quantum ( radiation is dep5d5t on ! frequ5cy ( ! oscillator1 v>y+ directly ) ! latt]4 ,if ?us we d5ote ! smalle/ quantity ( en]gy :i* an oscillator ( frequ5cy c emit or absorb by ,e1 !n we c write ,e h1 :]e h is a def9ite con/ant fix$ = all frequ5cies4 ,accord+ly ! cavity c receive radiation en]gy ( frequ5cy f ! radiat+ oscillators 9 its wall1 or transf] en]gy to ^! 9 no small] quantity ?an h4 ,! total en]gy ( t k9d emitt$ or absorb$ at any giv5 "t w always be an integral multiple ( h4 ,oscillators ) a frequ5cy #a times z great w emit en]gy 9 quanta :i* are #a times l>g]1 & s on4 ,! quantity h is indep5d5t1 n only ( ! wave-l5g?1 b also ( ! temp]ature & nature ( ! emitt+ body4 ,?is con/ant1 ! s-call$ ,planck con/ant1 is ?us a univ]sal con/ant4 ,if "o uses ! 8absolute0 units ( l5g?1 mass & "t 7see table1 p4 #baj71 its value comes out z #fed #aj4 ,= ! frequ5cy #gej #aj vibrations p] second1 correspond+ to ! extreme violet 9 ! visible spectrum1 ! ,planck en]gy quantum ?us becomes ab\t #e #aj erg1 or #cfi #aj foot-p\nds 7note t ! 8erg0 is ! 8absolute0 unit ( "w1 or ! am\nt ( "w done :5 a body is mov$ ?r\gh a di/ance ( #a cm4 by a =ce ( "o dyne act+ 9 ! direction ( ! motion1 :ile ! 8foot-p\nd0 is ! "w done :5 a =ce ( #a p\nd moves a body #a foot 9 ! direction ( ! =ce74 ,= light belong+ to ! r$ end ( ! spectrum1 ! en]gy is ab\t half z great4 ,if we pass1 h[ev]1 to ! highe/ frequ5cies & ! %orte/ wave-l5g?s :i* are kn[n1 namely ^? correspond+ to ! 8h>de/0 7i4e4 mo/ p5etrat+7 -rays 7see p4 #gh71 we meet ) en]gy quanta :i* are a million times l>g]1 i4e4 #b #aj erg1 al?\gh !y are /ill v small comp>$ to any am\nt ( en]gy measurable me*anically4 ,?is rem>kable !ory ( quanta1 :i* 9 ! h&s ( ,planck /ill possess$ a r ab/ract "*1 prov$ "u ,e9/e9's +5i\s treatm5t to h ! greate/ significance 9 _m problems :i*1 l heat radiation1 _h provid$ physici/s ) _m difficulties4 ,= by assum+ t en]gy 9 g5]al c\ld only be giv5 up & tak5 9 9 quanta1 c]ta9 facts ab\t ! specific heats ( bodies c\ld be acc\nt$ =--facts :i* ! old] physics _h prov$ p[]less to expla94 ,! ,planck en]gy quanta1 z ,e9/e9 %[$1 c\ld also expla9 9 a v direct & satisfactory way ! photoelectric effect1 z x is call$4 ,?is effect consi/s 9 ! free+ ( electrons f a metal plate :i* ultra-violet rays are all[$ to /rike4 ,! maximum velocity ) :i* ^! electrons are propell$ f ! plate is f\nd to be indep5d5t ( ! int5sity ( ! incid5t light1 b dep5d5t simply on ! frequ5cy ( ! radiation4 ,c>eful measurem5ts h inde$ %[n1 z ,e9/e9 pr$ict$1 t ! incid5t light really does utilize an en]gy quantum h to free ea* electron & give x velocity 7cf4 p4 #agb74 ,( ! diff]5t me?ods :i* n[adays are at h&1 ! photoelectric effect con/itutes "o ( ! be/ means ( det]m9+ ! value ( h4 ,x has be5 appli$ = t purpose by ,millikan1 to ^: +5i\s exp]im5ts ! mo/ accurate direct det]m9ation ( h is actually due4 ,all ?is lay completely outside ! laws ( electrodynamics1 & po9t$ to ! exi/5ce ( unkn[n & m fundam5tal laws4 ,b1 = ! "t be+1 physici/s _h to be satisfi$ m]ely ) a recognition ( ! fact t ^! my/]i\s en]gy quanta play a v significant "p 9 _m ph5om5a4 ,a decade ago physics1 z reg>ds radiation problems1 0 9 a v unsettl$ /ate2 ) f\r sep>ate bran*es ( k1 ea* ( :i* seem$ firm & well-f\nd$ en\gh 9 itself1 b :i* _h no common connect+ l9k1 inde$1 7 ev5 to "s ext5t inconsi/5t ) ea* o!r4 ,! fir/ ( ^! 0 ! classical electrodynamics surm\nt$ by ! felicit\s electron !ory ( ,lor5tz & ,l>mor4 ,! second 0 ! empirical k ( ! spectra re/+ on ! "w ( ,balm]1 ,ritz & ,rydb]g4 ,! ?ird 0 ,ru!r=d's nucle> atom model4 ,& ! f\r? 0 ,planck's quantum !ory ( heat radiation4 ,x 0 q evid5t t progress 9 ! !ory ( radiation & ! /ructure ( ! atom 0 hopeless z long z ^! f\r po9ts ( view rema9$ uncorrelat$4 ,ma9 ,outl9es ( ! ,bohr ,!ory4 ,su* 0 ! situation :51 9 #aiac1 ,bohr publi%$ 8 atomic !ory1 9 :i* he 0 able ) great +5uity to unite ! nucle> atom1 ! ,balm]-,ritz =mula & ! quantum !ory4 ,z f> z electrodynamics is conc]n$1 ! impossibility ( reta9+ t 9 its classical =m 0 pres5t$ 9 a mu* cle>] way ?an ev] be=e4 ,b1 z w pres5tly be evid5t1 ! ,bohr !ory has a v def9ite connection ) ! classical !ory1 & ,bohr's attempts to pres]ve & develop ?is connection h prov$ to be ( ! greate/ significance = 8 !ory4 ,9 spite ( ! fundam5tal rupture ) ! old ideas1 ! ,bohr !ory /rives to absorb all t is useful 9 ! classical po9t ( view4 ,at ! head ( ! !ory appe> ! two fundam5tal hypo!ses or po/ulates on ! prop]ties ( ! atom4 ,! fir/ po/ulate /ates t = ea* atom or atomic sy/em !re exi/s a numb] ( def9ite /ates ( motion1 call$ 8/ation>y /ates10 9 :i* ! atom 7or atomic sy/em7 c exi/ )\t radiat+ en]gy4 ,a f9ite *ange 9 ! en]gy cont5t ( ! atom c take place only 9 a process 9 :i* ! atom passes completely f "o /ation>y /ate to ano!r4 ,! second po/ulate /ates t if su* a transition takes place ) ! emission or absorption ( electromagnetic light waves1 ^! waves w h a def9ite frequ5cy1 ! magnitude ( :i* is det]m9$ by ! *ange 9 ! en]gy cont5t ( ! atom4 ,if we d5ote ! *ange 9 en]gy by ,e & ! frequ5cy by we may write ,e ,e h1 or ----- h :]e h is ! ,planck con/ant4 ,9 consequ5ce ( ! second po/ulate ! emission z well z ! absorption ( en]gy by ! atom always takes place 9 quanta4 ,! two po/ulates say no?+ conc]n+ ! nature ( ! motion 9 ! /ation>y /ates4 ,9 ! applications1 h[ev]1 a connection ) ! ,ru!r=d atomic model is e/abli%$4 ,conf9+ our att5tion fir/ to ! hydrog5 atom1 ! sy/em ) :i* we are conc]n$ consi/s1 accord+ly1 ( a positive nucleus & "o electron revolv+ ab\t x4 ,! v>i\s /ates ( motion :i* ! electron c assume 9 virtue ( ! fir/ po/ulate are a s]ies ( orbits at diff]5t di/ances f ! nucleus4 ,9 ea* ( ^! 8/ation>y orbits0 ! electron foll[s ! g5]al me*anical laws ( motion2 i4e4 "u ! nucle> attraction :i* is inv]sely proportional to ! squ>e ( ! di/ance1 ! electron describes an ellipse ) ! nucleus at "o focus1 z has previ\sly be5 /at$2 b 9 contradiction ) ! classical electrodynamics x w emit no radiation :ile mov+ 9 ?is orbit4 ,fig4 #be %[s a s]ies ( ^! orbits1 to :i* ! numb]s #a1 #b1 #c1 #d h be5 atta*$1 & :i* = simplicity are repres5t$ z circul>4 ,illu/ration3 ,,fig4 #be4--,! ,bohr model ( ! hydrog5 atom 9 ! simplifi$ =m 7) circles in/ead ( ellipses74 ,if ! electron passes f an out] orbit to an inn] "o2 = example1 if x goes f numb] #d to numb] #b1 or f numb] #b to numb] #a1 ! electric =ce :i* attracts x to ! nucleus w d "w j z ! =ce ( gravity does "w :5 a /one falls to ! gr\nd4 ,a "p ( ?is "w is us$ to increase ! k9etic en]gy ( ! electron1 mak+ its velocity 9 ! inn] orbit great] ?an 9 ! out]1 b ! re/ ( ! "w is trans=m$ into radiation en]gy :i* is emitt$ f ! atom 9 ! =m ( mono*romatic light4 ,9 consequ5ce ( ! second po/ulate ! frequ5cy ( ! emitt$ radiation is proportional to ! en]gy loss4 ,:5 ! electron has rea*$ ! inn]mo/ orbit 7! "o d5ot$ by #a 9 ! figure71 x _c get any ne>] ! nucleus & h5ce _c emit any m radiation unless x fir/ is impell$ to pass f its inn] orbit to an out] orbit aga9 by ! absorption ( ext]nal en]gy suffici5t to br+ ab\t ?is *ange4 ,once 9 ! out] orbit aga91 x is 9 a /ate to produce radiation by fall+ 9 a second "t4 ,! inn]mo/ orbit repres5ts ?us ! electron's equilibrium /ate1 & corresponds to ! normal /ate ( ! atom4 ,if we try to illu/rate ! matt] ) an analogy f ! !ory ( s\nd1 we c d s by comp>+ ! atom n ) a /r+$ in/rum5t1 b ) a hypo!tical musical in/rum5t ( a :olly diff]5t k9d4 ,let u imag9e t we h plac$ "o ov] ano!r & conc5trically a s]ies ( circul> discs ( progressively small] radii1 & let u suppose t a small sph]e c move ar\nd any "o ( ^! )\t friction & )\t emitt+ s\nd4 ,9 su* a motion ! sy/em may be said to be 9 a 8/ation>y /ate40 ,soon] or lat] ! sph]e may fall f ! fir/ disc on to "o l[] d[n & cont9ue to roll ar\nd on ! second1 hav+ emitt$ a s\nd1 let u assume1 by its fall4 ,by pass+ ?us f "o /ation>y /ate to ano!r x loses a quantity ( en]gy equal to ! "w :i* w\ld be necess>y to raise x aga9 to ! disc previ\sly occupi$1 & to br+ x back to ! orig9al /ate ( motion4 ,we c assume t ! en]gy :i* is lo/ 9 ! fall reappe>s 9 a s\nd wave emitt$ by ! in/rum5t1 & t ! pit* ( ! s\nd emitt$ is proportional to ! en]gy s5t out4 ,if1 moreov]1 we imag9e t ! l[]mo/ disc is groov$ 9 su* a way t ! sph]e _c fall f>!r1 !n ?is fanciful in/rum5t c provide a v r\gh analogy ) ! ,bohr atom4 ,we mu/ bew>e1 h[ev]1 ( /ret*+ ! analogy f>!r ?an is "h indicat$4 ,x mu/ be specially emphasiz$ "h t ! frequ5cy ( ! s\nd emitt$ 9 ! above example has no connection ) ! frequ5cy ( revolution ( ! sph]e4 ,9 ! ,bohr atom1 likewise1 ! frequ5cy ( revolution ( ! electron 9 its /ation>y orbit has no direct connection ) ! frequ5cy ( ! radiation emitt$ :5 ! electron passes f ?is orbit to ano!r4 ,?is is a v surpris+ break ) all previ\s views on radiation1 a break ^: revolution>y "* %\ld n be "u-e/imat$4 ,b1 h[ev] unreasonable x might seem to give up ! direct connection betwe5 ! revolutional frequ5cy & ! radiation frequ5cy1 x 0 absolutely necess>y if ! ,ru!r=d atomic model 0 to be pres]v$4 ,& z we %all n[ see1 ! new po9t ( view ( ! ,bohr !ory leads naturally to an int]pretation ( ! ,balm]-,ritz =mula1 :i* _h previ\sly n be5 connect$ ) any o!r physical !ory4 ,! quantity ( en]gy ,e1 :i* ! atom gives up :5 ! electron passes f an out] to an inn] orbit1 or :i*1 conv]sely1 is tak5 9 :5 ! electron passes f an inn] to an out] orbit1 may1 z has be5 indicat$1 be reg>d$ z ! diff]5ce betwe5 ! en]gy cont5ts ( ! atom 9 ! two /ation>y /ates4 ,?is diff]5ce may be express$ 9 ! foll[+ way4 ,let u imag9e t we eject ! electron f a giv5 orbit 7e4g4 ,no4 #b 9 ! diagram7 s t x is s5t to 8inf9ity10 or1 9 o!r words1 is s5t s f> away f ! nucleus t ! attraction ( ! latt] becomes negligible4 ,to br+ ab\t ?is removal ( ! electron f ! atom dem&s a c]ta9 am\nt ( en]gy1 :i* we c call ! ioniz+ "w correspond+ to ! /ation>y orbit 9 "q4 ,we may "h designate x z ,a4 ,to eject ! electron f ! orbit ,no4 #d w dem& a small] am\nt ( ioniz+ "w1 ,a4 ,! diff]5ce ,a - ,a is accord+ly ! "w :i* mu/ be done to transf] ! electron f ! orbit ,no4 #b to ! orbit ,no4 #d4 ,?is is1 h[ev]1 exactly equal to ! quantity ,e ( en]gy :i* w be emitt$ z light :5 ! electron passes f orbit ,no4 #d to orbit ,no4 #b4 ,if we call ! frequ5cy ( ?is light 1 !n f ! relations ,e h & ,e ,a - ,a1 we h h ,a - ,a ,if1 n[1 9 place ( ?is specific example us+ ! /ation>y orbits #b & #d we take any two orbits designat$ by ! numb]s n 7= ! inn]7 & n 7= ! out]71 we c write = ! frequ5cy ( ! radiation emitt$ = a transition betwe5 ^! arbitr>y /ates h ,a - ,a or ,a ,a ----- - ----- h h ,we h n[ rea*$ ! po9t :]e we ought to br+ 9 ! ,balm]-,ritz =mula = ! di/ribution ( ! l9es 9 ! hydrog5 spectrum4 ,?is =mula may be writt5 7see p4 #ei7 ,k ,k ------ - ----- n n ,we c n[ see v cle>ly ! simil>ity betwe5 ! =mula d]iv$ f ! spectrum inve/igations & t d]iv$ f ! two ,bohr po/ulates4 ,9 bo? =mul ! frequ5cy appe>s z ! diff]5ce betwe5 two t]ms :i* are *>act]iz$ 9 bo? cases by two integral numb]s1 9 ! fir/ =mula1 numb]s d5ot+ two /ation>y orbits 9 ! ,bohr model = hydrog51 & 9 ! second ! two numb]s :i* 9 ! ,balm]-,ritz =mula = ! hydrog5 spectrum *>act]ize1 respectively1 a s]ies & "o ( ! l9es ( ! s]ies4 ,to obta9 complete agreem5t we h m]ely to equate ! correspond+ t]ms 9 ! two =mul4 ,?us we h = any arbitr>y integ] n ,a ,k ----- ---- or h n h,k ,a ------ n ,= ! inn]mo/ /ation>y orbit1 = :i* n #a1 ! ioniz+ "w ,a w accord+ly be equal to ! product ( ! con/ants h & ,k ( ,planck & ,balm] respectively2 & = ! orbits ,no4 #b1 ,no4 #c1 ,no4 #d1 etc41 ! values w be respectively 1 _/1 _/1 etc41 ( ?is product4 ,f ! *>ges on ! nucleus & ! electron1 :i* are bo? equal to ! elem5t>y quantum e ( electricity 7see p4 #ij71 & f ! ioniz+ en]gy = a giv5 orbit we c n[ f9d by ! use ( simple me*anical consid]ations ! radius ( ! orbit4 ,if we d5ote ! radii ( ! orbits #a1 #b1 #c 444 by a1 a1 a 4441 we !n obta9 = ! diamet]s #b;a1 #b;a1 #b;a 444 ! values #b;a #ajef #aj cm4 7or approximately #b;a #aj cm471 #b;a #d #aj cm41 #b;a #i #aj cm41 etc4 ,x is se5 t ! radii ( ! orbits are 9 ! proportion #a1 #d1 #i 4441 or 9 o!r words ! squ>es ( ! integ]s :i* det]m9e ! orbit numb]s4 ,x is 9 ?is proportion t ! circles 9 ,fig4 #be are drawn4 ,we mu/ rememb]1 h[ev]1 t we h "h = ! mom5t be5 ?9k+ ( ! orbits z circles1 :ile 9 reality !y mu/ 9 g5]al be assum$ to be ellipses4 ,! =ego+ consid]ations w1 h[ev]1 /ill hold ) ! s+le *ange t #b;a w n[ mean1 in/ead ( ! diamet] ( a circle1 ! major axis ( an ellipse4 ,let u return to ! =mul ,a ,a ----- - ---- h h ,k ,k & ------ - ----- n n ,"h n d5otes 9 ! fir/ =mula ! index numb] = ! inn] ( ! two orbits betwe5 :i* ! transition is suppos$ to take place1 :ile 9 ! second =mula n d5otes a def9ite s]ies 9 ! hydrog5 spectrum4 ,if n is #b :ile n takes on ! values #c1 #d1 #e 444 !n 9 ! ,bohr model ( ! hydrog5 atom ?is corresponds to a s]ies ( transitions to ! orbit ,no4 #b f ! orbits #c1 #d1 #e 4441 :ile 9 ! hydrog5 spectrum ?is corresponds to ! l9es 9 ! ,balm] s]ies1 namely1 ! r$ l9e 7,h7 correspond+ to ! transition #c-b1 ! blue-gre5 l9e 7,h7 to #d-b1 ! violet l9e 7,h7 to #e-b & s on4 ,if we n[ put n #a :ile n takes ! values #b1 #c1 #d 4441 we get 9 ! atom transitions to ! orbit ,no4 #a f ! orbits ,no4 #b1 #c1 #d 4441 correspond+ 9 ! spectrum to :at is call$ ! ,lyman s]ies 9 ! ultra-violet 7nam$ aft] ! ,am]ican physici/ ,lyman1 :o has c>ri$ on ext5sive rese>*es 9 ! ultra-violet region ( ! spectrum74 ,?us e l9e 9 ! hydrog5 spectrum is repres5t$ by a transition betwe5 two def9ite /ation>y /ates 9 ! hydrog5 atom1 s9ce ?is transition w give ! frequ5cy correspond+ to ! l9e 9 "q4 ,at fir/ sight ?is w\ld seem p]haps to be su* an extraord9>y satisfactory result t x w\ld prove an ov]:elm+ witness 9 fav\r ( ! ,bohr !ory4 ,a little m c>eful ?\ght1 on ! o!r h&1 w\ld p]haps cause a complete rev]sion f en?usiasm & lead "s to say t ! :ole ?+ has n ! slighte/ value1 because ! /ation>y /ates 7 s *os5 t agreem5t might be made ) ! ,balm]-,ritz =mula4 ,?is la/ consid]ation1 inde$1 /ates ! tru? 9 s f> t ! agreem5t betwe5 ! =mula & ! !ory1 at lea/ z develop$ "h up to ?is po9t1 is ( a purely =mal nature4 ,9 ! ,bohr po/ulates ! frequ5cies ( ! emitt$ radiation are det]m9$ by a diff]5ce betwe5 two ( a s]ies ( en]gy quantities1 *>act]iz+ ! /ation>y /ates1 j z 9 ! ,balm]-,ritz =mula !y appe> z a diff]5ce betwe5 two ( a s]ies ( t]ms 7,k1 ,k_/#d1 ,k_/#i1 4447 ea* *>act]iz$ by its integ]4 ,n[ by *>act]iz+ ! quantities ( en]gy 9 ! /ation>y /ates by a s]ies ( integ]s 79 itself a :olly arbitr>y proc$ure7 complete agreem5t betwe5 ! ,bohr /ation>y /ates idea & ! spectral =mul c be atta9$4 ,x is n ev5 necess>y to introduce ! ,ru!r=d atomic model to atta9 ?is end4 ,by br++ 9 ?is specific model1 "o might jo9 ! new !ory to ! k already ga9$ ( ! atomic /ructure1 &1 s to speak1 cry/allize ! hi!rto undef9$ or only vaguely def9$ /ation>y /ates into m def9ite =m z revolution 9 c]ta9 concrete orbits4 ,?is w\ld !n lead to a m compreh5sive conception ( atomic /ructure4 ,b ! !ory un=tunately w\ld /ill be r arbitr>y1 s9ce !re w\ld seem to be no ju/ification = pick+ out c]ta9 fix$ orbits ) def9ite diamet]s or major axes to play a special rle4 ,"o _c wond] !n t _m sci5ti/s consid]$ ! ,bohr !ory unacceptable1 or at any rate 7 incl9$ to look ^u x simply z an arbitr>y1 unreasonable conception :i* really expla9$ no?+4 ,naturally1 ,bohr himself cle>ly recogniz$ ! =mal nature ( ! agreem5t betwe5 ! ,balm]-,ritz =mula & 8 po/ulates4 ,b ,bohr 0 ! fir/ to see t ! quantum !ory af=d$ ! possibility ( br++ ab\t su* an agreem5t1 & he saw1 moreov]1 t ! agreem5t 0 n m]ely =tuit\s1 b conta9$ )9 x some?+ really fundam5tal1 on :i* "o c\ld build fur!r4 ,t atomic processes on 8 !ory took on an unreasonable "* 7comp>$ ) ! classical !ory7 0 no?+ to worry ab\t1 = ,bohr _h come to ! cle> recognition t x 0 completely impossible to und]/& f kn[n laws ! ,planck-,e9/e9 8quantum radiation10 or to d$uce ! prop]ties ( ! spectrum f ! ,ru!r=d atom alone4 ,he !re=e saw t 8 !ory 0 really n introduc+ new improbabilities1 b 0 only caus+ ! fundam5tal nature ( ! contradictions :i* _h previ\sly h9d]$ developm5t 9 ?is field to appe> 9 a cle>] light4 ,b 9 addition to ?is ! *oice ( ! dim5sions ( ! /ation>y /ates 0 by no means s arbitr>y z might appe> 9 ! =ego+4 ,9 8 fir/ pres5tation ( ! !ory ( ! hydrog5 spectrum1 ,bohr _h d]iv$ 8 results f c]ta9 consid]ations connect$ ) ! quantum !ory--consid]ations ( a purely =mal nature1 inde$1 j z ^? develop$ 9 ! prec$+1 b lead+ to agreem5t ) ! spectral =mul4 ,he1 moreov]1 call$ att5tion to ! fact t ! values obta9$ = ! orbital dim5sions 7 ( ! same ord] ( magnitude z ^? :i* c\ld be expect$ on :olly diff]5t gr\nds4 ,! diamet] ( ! inn]mo/ orbit1 i4e41 t :i* def9es ! out] limit ( ! atom 9 ! normal /ate1 0 f\nd to be1 z has be5 not$ above1 ab\t #aj cm41 i4e41 ( ! same ord] ( magnitude z ! values obta9$ = ! diamet]s ( molecules on ! k9etic !ory ( gases 7see p4 #bg74 ,! /ation>y /ates correspond+ to v high quantum numb]s "o c\ld expect to meet only :5 hydrog5 0 v att5uat$1 = o!rwise !re c\ld be no room = ! l>ge orbits4 ,we note t ! #cbnd orbit mu/ h a diamet] #cb 7or ov] #ajjj times7 z great z ! inn]mo/ orbit4 ,s9ce1 n[1 l9es ) high numb] 9 a hydrog5 s]ies correspond on ! ,bohr !ory to transitions f orbits ( high numb] to an inn] orbit1 x became und]/&able :y only comp>atively few l9es ( ! ,balm] s]ies are ord9>ily obs]v$ 9 ! dis*>ge tube1 :ile _m m l9es are obs]v$ 9 ! spectra ( c]ta9 />s4 ,= 9 su* />s ! possibility is left op5 = hydrog5 to exi/ 9 a v att5uat$ /ate1 & yet 9 su* l>ge masses t ! l9es 9 "q c become /rong en\gh = obs]vation4 ,9 fact1 "o mu/ assume t 9 a great mass ( hydrog5 a v l>ge numb] ( atoms s5d out simultane\sly light ( ! wave-l5g? correspond+ to "o l9e4 ,= ! ioniz+ "w1 i4e41 ! "w necess>y to eject ! electron completely f ! normal /ate & ?us make ! atom into a positive ion1 ! ,bohr !ory gives a value ( ! same ord] ( magnitude z ! s-call$ 8ionization pot5tials0 :i* h be5 f\nd by exp]im5t = v>i\s gases4 ,an exact correspond5ce betwe5 !ory & exp]im5t c\ld = hydrog5 n be atta9$ ) c]ta9ty1 because ! hydrog5 atoms 9 hydrog5 gas "u ord9>y conditions always appe> unit$ 9 molecules4 ,9 8 v fir/ pap]1 h[ev]1 ,bohr _h /udi$ ,balm]'s =mula also f ano!r po9t ( view1 & _h d]iv$ 9 ?is way an expression = ! ,rydb]g con/ant ,k :i* agre$ ) exp]im5t4 ,^! consid]ations h ref]5ce to ! above-m5tion$ connection ( ! !ory ) ! classical !ory ( electrodynamics4 ,su* a connection _h previ\sly be5 kn[n to exi/ 9 ! fact t1 = long wave-l5g?s1 ! radiation =mula ( ,planck r$uces practically to ! ,rayleigh ,jeans ,law :i* c be d]iv$ f electrodynamics4 ,?is is relat$ to ! fact t :5 is small 7long wave-l5g?s71 ! en]gy quantum h is v small1 & h5ce ! "* ( ! radiation emitt$ w approa* m & m ne>ly to a cont9u\s 8unquantiz$0 radiation4 ,"o might !n expect t ! ,bohr !ory also %\ld lead 9 ! limit ( long wave-l5g?s & small frequ5cies to results resembl+ ^? ( ! ord9>y electrodynamic !ory ( ! radiation process4 ,on ! ,bohr !ory we get ! long wave-l5g?s = transitions betwe5 two /ation>y /ates ( high numb]s 7numb]s :i* also diff] little f ea* o!r74 ,?us suppose n is a v l>ge numb]4 ,!n ! transition f ! orbit n to ! orbit n - #a w give rise to radiation ( great wave-l5g?4 ,= 9 ?is case ,a & ,a diff] v little1 & accord+ly h is v small1 z mu/ be also4 ,accord+ to ! electrodynamic !ory ( radiation1 ! revolv+ electron %\ld emit radiation ^: frequ5cy is equal to ! electron's frequ5cy ( revolution4 ,accord+ to ! ,bohr !ory x is impossible to fulfil ?is condition exactly1 s9ce radiation results f a transition betwe5 two /ation>y orbits 9 ea* ( :i* ! electron has a di/9ct revolutional frequ5cy4 ,b if n is a l>ge numb]1 ! diff]5ce betwe5 ! frequ5cies ( revolution & = ! two orbits n & n - #a1 respectively1 becomes v small2 = example1 = n #ajj1 x is only #c p] c5t4 ,= a c]ta9 high value ( n1 !n1 ! frequ5cy ( ! emitt$ radiation c !re=e be approximately equal to ! frequ5cy ( revolution ( ! electron 9 bo? ! two orbits1 betwe5 :i* ! transition takes place4 ,b ev5 if ?is prov$ correct = values ( n ab\t #ajj1 "o c\ld n be sure be=eh& :e!r x w\ld "w out "r = /ill l>g] values ( n1 = example1 #ajjj4 ,9 ord] to inve/igate ?is latt] po9t we mu/ look into ! =mul = ! revolutional frequ5cy 9 a /ation>y orbit & = ! radiation frequ5cy 4 ,s9ce1 accord+ to ! ,bohr !ory1 we c apply ! usual laws ( me*anics to revolution 9 a /ation>y orbit1 x is an easy matt] to f9d an expression = 4 ,f a %ort ma!matical calculation we c d$uce t ,r_/n1 :]e ,r is ! frequ5cy ( revolution = ! fir/ orbit 7n #a74 ,we f9d 1 on ! o!r h&1 by sub/itut+ 9 ! ,balm]-,ritz =mula ! numb]s n & n - #a1 & a simple calculation %[s t = great values ( n1 ! expression = w approa* 9 ! limit ! simple =m #b,k_/nsup#c4 ,= l>ge orbit numb]s1 accord+ly v>ies z 1 i4e41 inv]sely proportional to ! ?ird p[] ( n1 & by equat+ ,r & #b,k1 we f9d t ! values = & t5d m & m to become equal4 ,9 ?is way ! value ( ,k1 ! ,balm] con/ant1 may be comput$4 ,x is f\nd t m ,k #b;e----- h :]e e is ! *>ge on ! electron1 m ! mass ( ! electron1 & h is ,planck's con/ant4 ,^u ! sub/itution ( ! exp]im5tal values = ^! quantities1 a value ( ,k is det]m9$ :i* agrees ) ! exp]im5tal value 7f ! spectral l9es inve/igation7 ( #cbi #aj )9 ! accuracy to :i* e1 m & h are obta9able4 ,?is agreem5t has f ! v fir/ be5 a significant support = ! ,bohr !ory4 ,"o might n[ object t we h "h consid]$ radiation due to a transition betwe5 two successive /ation>y /ates1 e4g41 ,no4 #ajj & ,no4 #ii1 or ! l 7a 8s+le jump0 we might call x74 ,on ! o!r h&1 = transitions betwe5 /ates ^: numb]s diff] by #b1 #c1 #d or m 7z 9 a d\ble jump1 or a triple jump7 ! agreem5t f\nd above w :olly disappe>1 & d\bt be ca/ on its value4 ,= 9 su* cases ( high orbit numb]s ! frequ5cy ( revolution w rema9 approximately ! same ev5 = a diff]5ce ( #b1 #c1 #d or m 9 orbit numb]2 b ! radiation frequ5cy = a d\ble jump w be ne>ly twice t = a s+le jump1 :ile t = a triple jump w be ne>ly ?ree times1 etc4 ,accord+ly1 = approximately ! same revolutional frequ5cy we %all h 9 ^! cases = ! radiation frequ5cy v ne>ly 1 #b1 #c1 etc4 ,we mu/1 h[ev]1 rememb] t :5 ! orbit 9 ! /ation>y /ates is n a circle1 b an ellipse 7z mu/ 9 g5]al be assum$ to be ! case71 ! classical electrodynamics require t ! electron emits besides ! 8fundam5tal0 radiation ( frequ5cy 1 ! ov]tones ( frequ5cies #b1 #c 4444 ,we !n also "h see ! outw>d simil>ity betwe5 ! ,bohr !ory & ! classical electrodynamics4 ,we may say t ! radiation ( frequ5cy 1 produc$ by a s+le jump1 corresponds to ! fundam5tal h>monic compon5t 9 ! motion ( ! electron1 :ile ! radiation ( frequ5cy 1 emitt$ by a d\ble jump1 corresponds to ! fir/ ov]tone1 etc4 ,! simil>ity is1 h[ev]1 only ( a =mal nature1 s9ce ! processes ( radiation1 accord+ to ! ,bohr !ory1 are ( q diff]5t nature ?an w\ld be expect$ f ! laws ( electrodynamics4 ,9 ord] to %[ h[ fundam5tal is ! diff]5ce1 ev5 :]e ! simil>ity seems greate/1 let u assume t we h a mass ( hydrog5 ) a v l>ge numb] ( atoms 9 orbits1 correspond+ to v high numb]s1 & t ! revolutional frequ5cy c practically be set equal to ! same quantity 4 ,!re may take place transitions betwe5 orbits ) ! diff]5ce #a1 #b1 #c 444 9 numb]1 & z ! result ( ^! diff]5t transitions we %all f9d1 by spectrum analysis1 9 ! emitt$ radiation frequ5cies :i* are practically 1 #b1 #c1 etc4 ,accord+ to ! radiation !ory ( electrodynamics we %\ld also get ^! frequ5cies & ! spectral l9es correspond+ to !m4 ,x mu/1 h[ev]1 be assum$ t !y are produc$ by ! simultane\s emission f e individual radiat+ atom ( a fundam5tal & a s]ies ( ov]tones4 ,accord+ to ! ,bohr !ory1 on ! o!r h&1 ea* individual radiat+ atom at a giv5 "t emits only "o def9ite l9e correspond+ to a def9ite frequ5cy 7mono*romatic radiation74 ,we c n[ realize t ! ,bohr !ory takes u into unkn[n regions1 t x po9ts t[>ds fundam5tal laws ( nature ab\t :i* we previ\sly _h no ideas4 ,! fundam5tal po/ulates ( electrodynamics1 :i* = a long "t seem$ to be ! fundam5tal laws ( ! physical _w itself1 by :i* !re 0 hope ( expla9+ ! laws ( me*anics & ( light & ( ev]y?+ else1 7 disclos$ by ! ,bohr !ory z m]ely sup]ficial & only applicable to l>ge-scale ph5om5a4 ,! app>5tly exact acc\nt ( ! activities ( nature1 obta9$ by ! =mul ( electrodynamics1 (t5 veil$ processes ( a nature entirely diff]5t f ^? ! =mul 7 suppos$ to describe4 ,"o might !n express "s surprise t ! laws ( electrodynamics c\ld h be5 obta9$ at all & int]pret$ z ! mo/ fundam5tal ( all laws4 ,x mu/1 h[ev]1 be rememb]$ t ! ,bohr !ory = l>ge wave-l5g?s1 i4e41 ! sl[ oscillations1 leads to a =mal agreem5t ) electrodynamics4 ,x mu/1 moreov]1 be rememb]$ t ! laws ( electrodynamics are e/abli%$ on ! basis ( l>ge-scale electric & magnetic processes :i* d n ref] to ! activities ( sep>ate atoms1 b 9 :i* v great numb]s ( electrons are c>ri$ 9 a c]ta9 direction 9 ! electric conductors or vibrate 9 oscillations :i* are extremely sl[ comp>$ ) light oscillations4 ,moreov]1 ! obs]v$ laws1 ev5 if !y c acc\nt = _m ph5om5a 9 light1 e>ly %[$ _! inability to expla9 ! nature ( ! spectrum & _m o!r problems connect$ ) ! detail$ /ructure ( matt]4 ,inde$ ! m ?is /ructure 0 /udi$1 ! great] became ! difficulties1 ! /rong] ! evid5ce t ! solution _c be obta9$ 9 ! classical way4 ,if we ask :e!r ,bohr has succe$$ 9 sett+ up new fundam5tal laws1 :i* c be quantitatively =mulat$1 to replace ! laws ( electrodynamics & to be us$ 9 ! d]ivation ( ev]y?+ t happ5s 9 ! atom & s 9 all nature1 ?is "q mu/ receive a negative answ]4 ,! motion ( ! electron 9 a giv5 /ation>y /ate may1 at any rate to a consid]able ext5t1 be calculat$ by ! laws ( me*anics4 ,we d n "k1 h[ev]1 :y c]ta9 orbits are1 9 ?is way1 pref]r$ ov] o!rs1 nor :y ! electrons jump f out] to inn] orbits1 nor :y !y sometimes g f "o /ation>y orbit to ! next & sometimes jump ov] "o or m orbits1 nor :y !y _c come any clos] to ! nucleus ?an ! inn]mo/ orbit1 nor :y1 9 ^! transitions1 !y emit radiation ( a frequ5cy det]m9$ accord+ to ! rules m5tion$4 ,x mu/ n be =gott5 t 9 sci5ce we mu/ always be pati5t ) ! "q 8,:y80 ,we c nev] get to ! bottom ( ?+s4 ,on acc\nt ( ! nature ( ! problem1 answ]s _c be giv5 to ! que/ions :y ! smalle/ mat]ial p>ticles 7= ! "t be+ hydrog5 nuclei & electrons7--! elem5t>y physical individuals--exi/1 or :y ! fundam5tal laws = _! mutual relation%ips--! mo/ elem5t>y relation%ips exi/+ betwe5 !m--are ( ?is or t nature2 a satisfactory answ] w\ld necess>ily ref] to some?+ ev5 m elem5t>y4 ,we _c claim m ?an a complete description ( ! relative positions & motions ( ! fundam5tal p>ticles & ( ! laws gov]n+ _! mutual action & _! int]play ) ! e!r4 ,if we exam9e our k ( ! atomic processes 9 ! light ( ?is ideal we are tempt$1 h[ev]1 to consid] x z b\ndless ignorance4 ,we are inconceivably f> f be+ able to give a description ( ! atomic me*anism1 su* z w\ld enable u to foll[1 = example1 an electron f place to place dur+ its entire motion1 or to consid] ! /ation>y /ates z l9ks 9 ! :ole in/ead ( isolat$ 8gifts f above40 ,dur+ ! transition f "o /ation>y /ate to ano!r we h no k at all ( ! exi/5ce ( ! electron1 inde$ we d n ev5 "k :e!r x exi/s at t "t or :e!r x p]haps is dissolv$ 9 ! e!r to be re-=m$ 9 a new /ation>y /ate4 ,b ev5 if we turn aside f su* a p>adoxical consid]ation1 x mu/ be recogniz$ t we d n "k :at pa? ! electron foll[s betwe5 two /ation>y orbits nor h[ long a "t ! transition takes4 ,z has be5 done 9 ?is book1 ! transition is (t5 d5ot$ z a jump1 & _m are incl9$ to believe t ! electron 9 its entire j\rney f a di/ant out] orbit to ! inn]mo/ sp5ds ! greate/ "p ( ! "t 9 ! /ation>y orbits1 :ile ea* transition takes b an inf9itesimally %ort "t4 ,?is1 h[ev]1 9 itself does n foll[ f ! !ory1 nor is x impli$ 9 ! expression 8! /ation>y /ates40 ,^! /ates may 9 a c]ta9 s5se be consid]$ z way /ations2 b :5 we ask :e!r an electron /ays long 9 ! /ation1 or :e!r ! /ation>y /ate is simply a transf] po9t :]e ! electron *anges its me?od ( travell+ s t ! frequ5cy ( its radiation is *ang$1 ^! are o!r matt]s1 & we _c "h g into ! consid]ations connect$ ) !m4 ,to get an idea ( "s ( ! difficulties inh]5t 9 ! attempt to make concrete pictures ( ! nature ( ! processes1 let u aga9 consid] ! analogy betwe5 ! ,bohr atom ( hydrog5 & a special k9d ( musical in/rum5t 9 :i* s\nds are produc$ by ! fall ( a small sph]e betwe5 discs at v>i\s heights 7see p4 #abj74 ,x w be mo/ natural "h to ?9k ( ! s\nds z develop$ by ! sph]e :5 x hits ! l[] disc1 & to ?9k ( ! tones ( high] pit* z giv5 by ! h>d] bl[s1 correspond+ to ! l>g] en]gy 7det]m9ative ( ! pit*7 releas$ by ! fall4 ,we c1 h[ev]1 by no means transf] su* a picture to ! atomic model4 ,= 9 ! latt] we _c ?9k ( ! /ation>y /ate z a mat]ial ?+ :i* ! electron c hit1 & x is also unreasonable to imag9e t ! radiation is n emitt$ until ! mom5t :5 ! transition is ov] & ! electron has arriv$ 9 its new /ation>y /ate4 ,we mu/1 on ! contr>y1 assume t ! emission ( radiation takes place dur+ ! :ole transition1 :e!r ! latt] consumes a %ort] or long] "t4 ,if x 7 ! case t a transition always took place betwe5 two successive /ation>y /ates1 x w\ld !n be possible to use ! musical in/rum5t to illu/rate ! matt]4 ,let u d5ote ! discs f ! l[e/ "o up ) ! numb]s #a1 #b1 #c1 444 correspond+ to ! /ation>y /ates #a1 #b1 #c1 444 & = ! mom5t consid] a fall f disc #f to disc #e4 ,we c n[ imag9e t ! space betwe5 ! two discs is 9 "s way tun$ = a def9ite note4 ,?us we might place betwe5 ! discs a s]ies ( %eets ( pap] hav+ su* int]vals betwe5 !m t ! sph]e 9 its fall /rikes _! edges at equal int]vals ( "t1 e4g41 _/ second4 ,! di/urbance !n set up w produce a s\nd ) ! frequ5cy #ajj vibrations p] second4 ,if ! di/ance betwe5 ! discs #e & #d is d\ble t betwe5 #f & #e1 ! sph]e 9 ! fall f #e to #d w lose d\ble ! en]gy lo/ 9 ! desc5t f #f to #e1 & w !re=e emit a note ( d\ble frequ5cy4 ,! %eets ( pap] 9 ! space betwe5 #e & #d mu/ !n be pack$ m tightly ?an betwe5 #f & #e4 ,& s ! space betwe5 any two discs may ?us be said to h its own p>ticul> classification or 8tun+40 ,9 analogy ) ?is we might ?9k ( ! space ab\t a hydrog5 nucleus divid$ by ! /ation>y /ates into sections ea* ) its own 8tun+40 ,b ap>t f ! intr9sic peculi>ity ( su* an arrangem5t & ! p>ticul> difficulties x w meet 9 try+ to expla9 ! m complicat$ ph5om5a to be m5tion$ lat]1 ! "o fact t ! electron 9 a transition f "o /ation>y /ate to ano!r c jump ov] "o or m int]v5+ /ation>y orbits1 makes su* a repres5tation impossible4 ,if ! sph]e 9 ! giv5 example c\ld fall f disc #f to disc #d1 x %\ld dur+ ! :ole desc5t emit a note ( high] pit* ?an 9 ! desc5t f #f to #e4 ,b ?is c\ld n possibly take place1 if ! space f #f to #e1 :i* mu/ be trav]s$ en r\te to #d1 is tun$ = a l[] note4 ,! same consid]ation applies to ! hydrog5 atom4 ,naturally x is n impossible to cont9ue ! ef=t to illu/rate ! matt] 9 "s concrete mann] 7"o might1 = example1 imag9e sep>ate *annels ea* ) its own p>ticul> tun+ betwe5 ! same two discs74 ,b 9 all ^! attempts ! situation mu/ become m & m complicat$ r ?an m simple4 ,on ! :ole x is v difficult to und]/& h[ a hydrog5 atom1 :]e ! electron makes a transition f orbit #f to orbit #d1 c dur+ ! entire transition emit a radiation ) a frequ5cy diff]5t f t :5 ! electron goes f orbit #f to orbit #e4 ,al?\gh x seems z if ! two electrons 9 mak+ ! transition are at fir/ "u id5tical conditions1 /ill1 nev]!less1 ! "o :i* is go+ to orbit #d emits f ! fir/ a radiation diff]5t f t emitt$ by ! "o go+ to orbit #e4 ,ev5 f ! v beg9n+ ! electron seems to arrange its conduct accord+ to ! goal ( its motion & also accord+ to future ev5ts4 ,b su* a gift is wont to be ! privilege ( ?9k+ be+s t c anticipate c]ta9 future occurr5ces4 ,! inanimate objects ( physics %\ld obs]ve causal laws 9 a m direct mann]1 i4e41 all[ _! conduct to be det]m9$ by _! previ\s /ates & ! contemporane\s influ5ces on !m4 ,!re is a difficulty ( a simil> nature 9 ! fact t f ! same /ation>y orbit ! electron sometimes />ts = a s+le jump1 ano!r "t = a d\ble jump1 & s on4 ,f c]ta9 consid]ations x is (t5 possible to prop\nd laws = ! probability ( ! diff]5t jumps1 s t = a great quantity ( atoms x is possible to calculate ! /r5g?s 7int5sities7 ( ! correspond+ spectral l9es4 ,b we c no m give ! reason :y "o giv5 electron at a giv5 "t det]m9es to make a d\ble jump :ile ano!r decides to make a s+le jump or n to jump at all1 ?an we c say :y a c]ta9 radium nucleus among _m explodes at a giv5 mom5t 7cf4 p4 #ajb74 ,?is simil>ity betwe5 ! occurr5ce ( radiation processes on ! ,bohr !ory & ( ! radioactive processes has especially be5 emphasiz$ by ,e9/e94 ,x mu/1 by no means1 be said t ! causal laws d n hold = ! atomic processes1 b ! h9ts giv5 "h indicate h[ difficult x w be to rea* an und]/&+--9 ! usual s5se--( ^! processes & consequ5tly ( ! processes ( physics 9 g5]al4 ,!re is mu* t might indicate t1 on ! :ole1 x is impossible to obta9 a consi/5t picture ( atomic processes 9 space & "t ) ! help ( ! motions ( ! nuclei & ! electrons & ! v>iations 9 ! /ate ( ! e!r1 & ) ! application ( su* fundam5tal conceptions ( physics z mass1 electric *>ge & en]gy4 ,ev5 if ?is 7 ! case1 x does n foll[ t a compreh5sive description 9 "t & space ( ! physical processes is impossible 9 pr9ciple2 b ! hope ( atta9+ su* a description mu/ p]haps be alli$ to ! repres5tation ( 8physical individuals0 or mat]ial p>ticles ( an ev5 l[] ord] ( magnitude ?an ! smalle/ p>ticles n[ kn[n--electrons & hydrog5 nuclei--& to ideas ( m fundam5tal nature ?an ^? n[ kn[n2 we are "h outside our pres5t sph]e ( exp]i5ce4 ,f all ! above rem>ks x w\ld be v easy to get ! impression t ! ,bohr !ory1 :ile x gives u a glimpse into dep?s previ\sly unsuspect$1 at ! same "t leads u into a fog1 :]e x is impossible to f9d ! way4 ,?is is v f> f be+ ! case4 ,on ! contr>y1 x has ?r[n new light on a ho/ ( physical ph5om5a ( diff]5t k9ds s t !y n[ appe> 9 a coh]5ce previ\sly unatta9able4 ,t ?is light is n deceptive foll[s f ! fact t ! !ory1 :i* has be5 gradually develop$ by ,bohr & _m o!r inve/igators1 has made x possible to pr$ict & to acc\nt = _m ph5om5a ) rem>kable accuracy & 9 complete agreem5t ) exp]im5tal obs]vation4 ,! fundam5tal concepts are1 on ! "o h&1 ! /ation>y /ates1 :]e ! usual laws ( me*anics c be appli$ 7al?\gh only )9 c]ta9 limits71 &1 on ! o!r1 ! 8quantum rule0 = transitions betwe5 ! /ates4 ,b at ! v beg9n+ x has be5 necess>y 9 _m respects to grope 9 ! d>k1 guid$ 9 "p by ! exp]im5tal results & 9 "p by v>i\s assumptions1 (t5 v arbitr>y4 ,= ,bohr himself1 a mo/ important guide has be5 ! s-call$ correspond5ce pr9ciple1 :i* expresses ! previ\sly m5tion$ connection ) ! classical electrodynamics4 ,x is difficult to expla9 9 :at x consi/s1 because x _c be express$ 9 exact quantitative laws1 & x is1 on ?is acc\nt1 also difficult to apply4 ,9 ,bohr's h&s x has be5 extraord9>ily fruitful 9 ! mo/ v>i$ fields2 :ile o!r m def9ite & m easily applicable rules ( guidance h inde$ giv5 important results 9 individual cases1 !y h %[n _! limitations by fail+ 9 o!r cases4 ,we c "h m]ely indicate :at ! correspond5ce pr9ciple is4 ,z has be5 said 7cf4 p4 #acj71 x has be5 f\nd t 9 ! limit+ region 7suffici5tly l[ frequ5cies7 :]e ! ,bohr !ory & ! classical electrodynamics are m]g$ 9 _! outw>d features1 a s]ies ( frequ5cies 1 1 = mono*romatic radiation1 emitt$ by diff]5t atoms 9 ! s+le jumps1 d\ble jumps1 etc41 ( ! electrons1 are equal to ! frequ5cies 1 #b1 #c 444 :i*1 accord+ to ! laws ( electrodynamics1 are conta9$ 9 ea* ( ^! atoms respectively z fundam5tal & ! fir/1 second 444 ov]tones 9 ! motion ( ! electron4 ,f>!r away f ?is region ! two sets ( frequ5cies are no long] equally l>ge1 b x is easy to und]/&1 f ! =ego+1 ! mean+ ( ! /atem5t t1 = example1 ! radiation ( a triple jump ) ! frequ5cy 8corresponds0 to ! second ov]tone #c 9 ! revolution ( ! electron4 ,x is ?is correspond5ce :i* ,bohr traces back to ! regions :]e !re is ev5 a great diff]5ce 9 two successive orbits & :]e ! frequ5cy produc$ by a transition betwe5 ^! orbits is v diff]5t f ! frequ5cies ( revolution 9 ! two orbits or _! ov]tones4 ,he expresses himself z foll[s3 8,! probability = ! occurr5ce ( s+le1 d\ble1 triple jumps1 etc41 is condition$ by ! pres5ce 9 ! motion ( ! atom ( ! diff]5t con/itu5t h>monic vibrations hav+ ! frequ5cy ( ! fundam5tal1 fir/ ov]tone1 second ov]tone1 etc41 respectively40 ,9 ord] to und]/& h[ ?is 8correspond5ce10 app>5tly s indef9ite1 c be us$ to d]ive important results1 we %all give an illu/ration4 ,let u assume t ! me*anical !ory = ! revolution ( an electron 9 ! hydrog5 atom _h l$ to ! result t ! orbits ( ! electrons always _h to be circles4 ,accord+ to ! laws ( electrodynamics1 ! motion ( ! electron w\ld 9 ?is case nev] give any ov]tones1 &1 accord+ to ! correspond5ce pr9ciple1 !re c\ld n appe> among ! frequ5cies emitt$ by hydrog5 any :i* w\ld correspond to ! ov]tones1 i4e41 !re w\ld n be any d\ble jumps1 triple jumps1 etc41 produc$1 b ! only transitions w\ld be ^? betwe5 successive /ation>y orbits4 ,! inve/igation ( ! spectrum %[s1 h[ev]1 t multiple jumps occur z well z s+le jumps1 & ?is fact may be tak5 z evid5ce t ! orbits 9 ! hydrog5 atom are n usually circles4 ,let u next assume t1 in/ead1 we _h obta9$ ! result t ! orbits ( ! electrons are always ellipses ( a c]ta9 q def9ite ecc5tricity1 correspond+ to c]ta9 def9ite ratios 9 int5sity betwe5 ! ov]tones & ! fundam5tals2 t1 = in/ance1 ! int5sity ( ! classical radiation due to ! fir/ ov]tone is 9 all /ates ( motion always "o-half t due to ! fundam5tal1 ! int5sity due to ! second ov]tone always "o-?ird t due to ! fundam5tal1 etc4 ,!n ! radiation actually emitt$ %\ld1 accord+ to ! correspond5ce pr9ciple1 be su* t ! int5sities ( ! l9es correspond+ to ! d\ble & triple jumps1 :i* />t f a giv5 /ation>y /ate1 are respectively "o-half & "o-?ird ( ! int5sity correspond+ to a s+le jump f ! same /ate4 ,by ^! examples we c obta9 an idea ( h[ ! correspond5ce pr9ciple may 9 c]ta9 cases acc\nt = v>i\s facts1 z to :at spectral l9es _c be expect$ to appe> at all1 al?\gh !y w\ld be giv5 by a p>ticul> transition1 & conc]n+ ! di/ribution ( int5sities 9 ^? :i* really appe>4 ,! illu/ration giv5 above1 h[ev]1 has really no?+ mu* to d ) actual problems1 & objections may be rais$ to ! r\gh way 9 :i* ! illu/ration has be5 h&l$4 ,! correspond5ce pr9ciple has its p>ticul> prov9ce 9 m complicat$ electron motions ?an ^? :i* appe> 9 ! unp]turb$ hydrog5 atom--motions :i*1 unlike ! simple elliptical motion1 are n compos$ ( a s]ies ( h>monic oscillations 71 #b1 #c 4447 b may be consid]$ z comp\nd$ ( oscillations ^: frequ5cies h o!r ratios4 ,! correspond5ce pr9ciple has1 9 su* cases1 giv5 rise to important discov]ies & pr$ictions :i* agree completely ) ! obs]vations4 ,we h dwelt ?us long ^u ! difficult correspond5ce pr9ciple1 because x is "o ( ,bohr's deepe/ ?\ghts & *ief guides4 ,x has made possible a m consi/5t pres5tation ( ! :ole !ory1 & x bids fair to rema9 ! key/one ( its future developm5t4 ,b f ^! g5]al consid]ations we %all n[ proce$ to m special phases ( ! problem & exam9e "o ( ! fir/ great triumphs 9 :i* ! !ory %[$ its ability to lead ! way :]e previ\sly !re _h be5 no pa?4 ,! ,false ,hydrog5 ,spectrum4 ,9 #ahig ! ,am]ican a/ronom]1 ,pick]+1 discov]$ 9 ! spectrum ( a />1 9 addition to ! usual l9es giv5 by ! ,balm] s]ies1 a s]ies ( l9es ea* ( :i* lay ab\t midway betwe5 two l9es ( ! ,balm] s]ies2 ! frequ5cies ( ^! l9es c\ld be repres5t$ by a =mula :i* 0 v simil> to ! ,balm] =mula2 x 0 necess>y m]ely to sub/itute n #c1 #d1 #e1 etc41 9 ! =mula on p4 #eg in/ead ( n #c1 #d1 #e1 etc4 ,x 0 lat] discov]$ t 9 _m />s !re 0 a l9e correspond+ to n _/ or n #b 9 ! usual ,balm]-,ritz =mula 7p4 #ei74 ,x 0 consid]$ t ^! mu/ be hydrog5 l9es1 & t ! spectral =mula = ?is elem5t %\ld prop]ly be writt5 #a #a ,k ---------- - --------- 7 n_/#b 7 7 n_/#b 7 :]e n & n c assume integral values4 ,?is 0 done s9ce x 0 n to be believ$ t ! spectral prop]ties ( *emically diff]5t elem5ts c\ld be s simil>4 ,?is view 0 v mu* /r5g!n$ :5 ,f[l]1 9 #aiab1 discov]$ ! ,pick]+ l9es 9 ! light f a vacuum tube conta9+ a mixture ( hydrog5 & helium4 ,x c\ld n q be und]/ood1 h[ev]1 :y ! new l9es did n 9 g5]al appe> 9 ! hydrog5 spectrum4 ,accord+ to ! ,bohr !ory = ! hydrog5 spectrum x 0 impossible--except by giv+ up ! agreem5t 7cf4 p4 #abi7 ) electrodynamics 9 ! region ( high orbit numb]s--to attribute to ! hydrog5 atom ! emission ( l9es correspond+ to a =mula :]e ! :ole numb]s 7 halv$4 ,! =mula giv5 above might1 h[ev]1 also be writt5 z 7 #a #a 7 #d,k7------ - ------74 7 n n 7 ,if ! e>li] calculations _h be5 c>ri$ out a little m g5]ally1 i4e41 if in/ead ( equat+ ! nucle> *>ge ) #a elem5t>y electric quantum e1 z 9 hydrog51 x _h be5 equat$ ) ,ne :]e ,n is an integ]1 !n ! frequ5cy might h be5 writt5 z 7 #a #a 7 ,n,k7------ - ------74 7 n n 7 ,?is =mula is evid5tly ! same z t j giv5 :5 ,n equals #b4 ,n[ we "k t helium has ! atomic numb] & nucle> *>ge #b 7cf4 p4 #ij72 a normal neutral helium atom has two electrons & x is1 !re=e1 v diff]5t f a hydrog5 atom4 ,if1 h[ev]1 a helium atom has lo/ "o electron & !re=e has become a positive ion ) "o *>ge1 x is a sy/em l ! hydrog5 atom ) only "o s+le electron mov+ ab\t ! nucleus4 ,x diff]s 9 its 8out]0 *>act]i/ics f ! hydrog5 atom only 9 hav+ a nucle> *>ge twice z great1 i4e4 its spectral =mula mu/ be giv5 ) ,n #b1 or ,n #d4 ,! =mula = ! suppos$ hydrog5 l9es w\ld consequ5tly fit ! case ( a helium atom :i* has lo/ an electron4 ,bohr 0 aw>e ( ?is1 & he !re=e sugge/$ t ! l9es 9 "q 7 due1 n to hydrog51 b to helium4 ,at fir/ all ! au?orities 9 ! field ( spectroscopy 7 aga9/ ?is view2 b mo/ ( ! d\bt 0 dispell$ :5 ,evans %[$ t ! l9es c\ld be produc$ 9 a vacuum tube :]e !re 0 only helium ) n a trace ( hydrog54 ,9 a lett] to ,nature 9 ,septemb] #aiac1 ,f[l] object$ to ! ,bohr !ory on ! gr\nd t ! disput$ l9e-=mula did n exactly correspond to ! =mula ) #d,k1 b t !re 0 a slight disagreem5t4 ,bohr's answ] 0 imm$iate4 ,he call$ att5tion to ! fact t--s9ce tempor>ily he _h s\ght only a fir/ approximation--9 8 calculations he _h tak5 ! mass ( ! nucleus to be inf9ite 9 comp>ison to ! mass ( ! electron1 s t ! nucleus c\ld be consid]$ exactly at ! focus ( ! ellipse describ$ by ! electron4 ,9 reality1 he said1 x mu/ be assum$ t nucleus & electron move ab\t _! common c5tre ( gravity1 j z 9 ! motion 9 ! sol> sy/em x mu/ be assum$ t n ! c5tre ( ! sun1 b ! c5tre ( gravity ( ! entire sy/em rema9s fix$4 ,?is motion ( ! nucleus leads to ! introduction ( a factor ,m_/7,m m7 9 ! expression = ! con/ant ,k giv5 on p4 #abi1 :]e ,m is ! mass ( ! nucleus & m t ( ! electron1 :i* 9 hydrog5 is t ( ! nucleus4 ,9 helium1 ,m is f\r times z l>ge z 9 hydrog51 s t ! giv5 factor "h has a slightly diff]5t value4 ,! diff]5ce 9 ! values = ,k = ! hydrog5 & = ! helium spectrum :i* 0 f\nd by ,f[l]1 is #jjd p] c5t41 :i* agrees exactly ) ! !oretical diff]5ce4 ,bohr ?us turn$ ,f[l]'s objection into a /rong argum5t 9 fav\r ( ! !ory4 ,! ,introduction ( m ?an "o ,quantum ,numb]4 ,dur+ ! fir/ ye>s aft] #aiac1 ,bohr 0 practically alone 9 work+ out 8 !ory1 at t "t /ill assail$ by _m1 & 9 %[+ its application to _m problems4 ,9 #aiaf1 h[ev]1 ! !ori/s 9 o!r c\ntries1 l$ by ! well-kn[n ,muni* pr(essor1 ,somm]feld1 began to associate !mselves ) ! ,bohr !ory1 & _! inve/igations gave rise to mu* ess5tial progress4 ,we %all "h m5tion "s ( ! mo/ important contributions4 ,9 ! !ory = ! hydrog5 spectrum prop\nd$ above1 x 0 assum$ t we _h to d ) a s+le s]ies ( /ation>y orbits1 ea* *>act]iz$ by its quantum numb]4 ,b z %[n by !oretical inve/igations ea* ( ! /ation>y orbits mu/1 :5 m detail is ask$ =1 also be indicat$ by an additional quantum numb]4 ,illu/ration3 ,,fig4 #bf4--;,a comp\nd electron motion produc$ by ! v rapid rotation ( an elliptical orbit4 ,?is is closely connect$ ) ! fact t ! motion ( ! electron is n q s simple z previ\sly assum$4 ,we h assum$ t ! electron moves ab\t ! nucleus j z a planet moves ab\t ! sun 7accord+ to ,kepl]'s ,laws71 9 an ellipse ) ! sun at "o focus1 s9ce ! electron is influ5c$ by an attraction inv]sely proportional to ! squ>e ( ! di/ance1 j z ! planets are attract$ by ! sun accord+ to ,newton's ,law4 ,we mu/1 h[ev]1 rememb] t we are "h conc]n$ ) ! electric attraction :i* at a giv5 di/ance is det]m9$1 n by mass1 b by ! electric *>ges 9 "q4 ,if ! latt] rema9 un*ang$1 :ile ! mass ( ! electron v>ies1 ! motion w be *ang$1 because ! same =ce has less effect ^u a great] mass4 ,accord+ to ! ,e9/e9 pr9ciple ( relativity1 ! mass ( ! electrons1 9 accordance ) ideas exp\nd$ long ago by ,j4 ,j4 ,?omson1 w n be con/ant1 b to a c]ta9 ext5t dep5d ^u ! velocity1 :i* w v>y f place to place1 :5 ! orbit is an ellipse4 ,z a result ( ?is1 ! motion becomes a c5tral motion ( m g5]al nature ?an a ,kepl] ellipse4 ,s9ce ! influ5ce ( ! *ange ( mass is v small1 ! orbit c /ill be consid]$ z an approximate ,kepl] ellipse2 b ! major axis w sl[ly rotate 9 ! plane ( ! orbit4 ,9 reality1 ! orbit w n !re=e be clos$1 b w h ! "* :i* is %[n 9 ,fig4 #bf2 ?is1 h[ev]1 corresponds to a mu* m rapid rotation ( ! major axis ?an t :i* actually takes place 9 ! hydrog5 atom1 :]e--ev5 9 case ( ! swifte/ rotation--! electron w revolve ab\t #dj1jjj times r\nd ! nucleus at ! same "t z ! major axis turns r\nd once4 ,if ! electron moves 9 a fix$ ,kepl] ellipse1 ! en]gy cont5t ( ! atom w be det]m9$ by ! major axis ( ! ellipse only4 ,if ^! axes = ! /ation>y /ates ) quantum numb]s #a1 #b1 #c 444 are respectively d5ot$ by #b;a1 #b;a1 #b;a 444 ! frequ5cy1 = in/ance1 9 ! transition f ,no4 #c to ,no4 #b--s9ce x is det]m9$ by ! loss ( en]gy--w be ! same :e!r ! orbits are circles or ellipses4 ,if1 on ! o!r h&1 ! electron moves 9 an ellipse :i* itself rotates sl[ly1 ! en]gy cont5t1 z c be %[n ma!matically1 w dep5d n only ^u ! major axis ( ! ellipse1 b also to a slight degree ^u its ecc5tricity1 or1 9 o!r words1 on its m9or axis4 ,!n 9 ! transition #c-b we %all get diff]5t en]gy losses & consequ5tly diff]5t frequ5cies1 accord+ z ! ellipse is m or less elongat$4 ,if x 7 ! case t ! ecc5tricity ( ! ellipses = a c]ta9 quantum numb] c\ld take arbitr>y values1 !n 9 ! transition betwe5 two numb]s we c\ld get frequ5cies :i* may take any value )9 a c]ta9 small int]val1 i4e41 a mass ( hydrog5 ) its great quantity ( atoms w\ld give diffuse spectral l9es1 i4e4 l9es :i* are broad5$ ov] a small cont9u\s spectral int]val4 ,?is is1 h[ev]1 n ! case2 b long be=e ! appe>ance ( ! ,bohr !ory x _h be5 discov]$ t ! hydrog5 l9es1 :i* we hi!rto h consid]$ z s+le1 possess :at is call$ a f9e /ructure4 ,) a spectroscopic app>atus ( high resolv+ p[] ea* l9e c be sep>at$ into two ly+ v close to ea* o!r4 ,?is f9e /ructure c n[ be expla9$ by ! fact t 9 a /ation>y /ate ) quantum numb] #c & major axis ( ! orbit #b;a1 = in/ance1 ! ecc5tricity ( ! orbit has nei!r "o s+le def9ite value nor all possible values1 b1 on ! contr>y1 x has sev]al discrete values ( def9ite magnitude1 to :i* !re correspond slightly diff]5t b def9ite values ( ! en]gy cont5t ( ! atom4 ,x is n[ possible to designate ! s]ies ( /ation>y orbits1 :i* h ! major axis #b;a ) ! pr9cipal quantum numb] #c1 ) subscripts giv+ ! auxili>y quantum numb] = /ation>y orbits correspond+ to ! diff]5t ecc5tricities1 s t ! s]ies is kn[n z #c1 #c1 #c4 ,in/ead ( a s+le l9e correspond+ to ! transition #c-b1 !re are !n obta9$ sev]al spectral l9es ly+ closely toge!r & correspond+ to transitions su* z #c-b1 #c-b1 etc4 ,by !oretical consid]ations1 requir+ consid]able ma!matical qualifications1 b ( ess5tially ! same =mal nature z ^? ,bohr _h orig9ally appli$ to ! det]m9ation ( ! /ation>y orbits 9 hydrog51 ,somm]feld 0 l$ to c]ta9 =mal quantum rules :i* p]mit ! fix+ ( ! /ation>y /ates ( ! hydrog5 atom correspond+ to su* a d\ble set ( quantum numb]s4 ,! results he obta9$ z reg>ds ! f9e /ructure ( ! hydrog5 l9es agree ) obs]vation inside ! limit ( exp]im5tal error4 ,al?\gh ,somm]feld's me?ods h also be5 v fruitful :5 appli$ to ! spectra ( o!r elem5ts1 !y 7 /ill ( a purely =mal & r arbitr>y nature2 x is1 !re=e1 ( great importance t ! ,leid5 pr(essor1 ,ehr5fe/1 & ,bohr succe$$ lat] 9 h&l+ ! problem f a m fundam5tal po9t ( view1 ,bohr mak+ use ( ! correspond5ce pr9ciple previ\sly m5tion$4 ,x %\ld be said "h1 by way ( sugge/ion1 t ,bohr us$ ! fact t ! motions ( ! electrons are n simple p]iodic b 8multiple p]iodic40 ,we see ?is mo/ simply if we ?9k ( ! revolution ( ! electrons 9 ! elliptical orbit z repres5t+ "o p]iod1 & ! rotation = ! major axis ( ! ellipse z repres5t+ a second p]iod4 ,illu/ration3 ,,fig4 #bg4--,! model ( ! hydrog5 atom ) /ation>y orbits correspond+ to pr9cipal quantum numb]s & auxili>y quantum numb]s4 ,fig4 #bg %[s a numb] ( ! possible /ation>y orbits 9 ! hydrog5 atom accord+ to ,somm]feld's !ory2 = ! sake ( simplicity ! orbits are drawn z completely clos$ ellipses4 ,if we exam9e1 = in/ance1 ! orbits ) pr9cipal quantum numb] #d1 we h "h ?ree m or less elongat$ ellipses1 #d1 #d1 #d1 & ! circle #d2 9 all ( !m ! major axis has ! same l5g?1 & ! l5g? ( ! major axis is to t ( ! m9or axis z ! pr9cipal quantum numb] is to ! auxili>y quantum numb] 7= ! circle #d 3 #d #a74 ,on ! :ole1 to a pr9cipal quantum numb] n !re correspond ! auxili>y quantum numb]s #a1 #b 444 n1 & ! orbit = :i* ! auxili>y quantum numb] equals ! pr9cipal quantum numb] is a circle4 ,we see t 9 ! m complicat$ hydrog5 atom model !re is possibility = a mu* great] numb] ( diff]5t transitions ?an 9 ! simple model 7,fig4 #be1 p4 #aai74 ,"s ( ! transitions are indicat$ by arr[s4 ,s9ce ! en]gy cont5t ( ! atom is almo/ ! same = orbits ) ! same pr9cipal quantum numb] & diff]5t auxili>y quantum numb]s1 ?ree transitions l #c-b1 #c-b & #c-b w give ab\t ! same frequ5cy1 & !re=e spectral l9es :i* lie v close toge!r4 ,9 a transition l #d-d ! emitt$ en]gy quantum h1 & also 1 w be s extremely small t ! correspond+ l9e w be too f> out 9 ! infra-r$ = any possibility ( obs]v+ x4 ,x mu/ be po9t$ out t ! above consid]ations only hold if ! hydrog5 atoms1 /rictly speak+1 are undi/urb$4 ,?us1 v small ext]nal =ces1 :i* may be due to ! neighb\rhood ( o!r atoms1 etc41 w be suffici5t to cause *anges 9 ! ecc5tricity ( ! /ation>y orbits4 ,9 su* a case ! above def9ition ( ! auxili>y quantum numb] becomes obvi\sly illusory1 & ! orig9al "* ( ! f9e /ructure disappe>s4 ,?is is 9 agreem5t ) ! exp]im5ts1 s9ce ! ,somm]feld f9e /ructure c be f\nd only :5 ! conditions 9 ! dis*>ge tube are especially quiet & fav\rable4 ,influ5ce ( ,magnetic & ,electric ,fields on ! ,hydrog5 ,l9es4 ,illu/ration3 ,,fig4 #bh4--,! splitt+ ( ?ree hydrog5 l9es "u ! influ5ce ( a /rong electric field4 ,z previ\sly m5tion$ 7p4 #gf71 ! spectral l9es are split into ?ree compon5ts :5 ! atoms emitt+ lights are expos$ to magnetic =ces4 ,! agreem5t f\nd "h betwe5 obs]vation & ! ,lor5tz electron !ory 0 consid]$ z /rong evid5ce ( ! correctness ( ! latt]4 ,accord+ to ! ,bohr !ory1 ! picture ^u :i* ?is explanation re/$ mu/ be ab&on$ entirely2 b =tunately x has be5 %[n t ! ,bohr !ory leads to ! same results2 &1 moreov]1 ,bohr1 ) ! assi/ance ( ! correspond5ce pr9ciple1 has be5 able to set =? ! m fundam5tal reason = ?is agreem5t4 ,! ,g]man sci5ti/1 ,/>k1 %[$1 9 #aiab1 t hydrog5 l9es are also split by electric fields ( =ce4 ,9 ,fig4 #bh x is %[n h[ v complicat$ ?is ph5om5on is2 "h ! classical electron !ory c\ld n at all expla9 :at happ5$4 ,?is ph5om5on c\ld also be acc\nt$ = by ! ext5d$ ,bohr !ory 7) ! introduction ( m ?an "o quantum numb]71 z x 0 %[n indep5d5tly by ,ep/e9 & by ,s*w>zs*ild 9 #aiaf2 fur!r1 ! correspond5ce pr9ciple has aga9 %[n its sup]iority1 s9ce x makes possible an approximate det]m9ation ( ! diff]5t int5sities ( ! diff]5t l9es4 ,a calculation c>ri$ out by ,h4 ,a4 ,kram]s has %[n t ! !ory gives a rem>kably good agreem5t ) ! exp]im5ts4 ,n until we ?9k ( ! extraord9>y accuracy ( ! measurem5ts :i* are obta9$ by spectrum analysis1 c we ?or\ghly appreciate ! importance ( ! quantitative agreem5t betwe5 !ory & obs]vation 9 ! hydrog5 spectrum t has j be5 m5tion$4 ,moreov]1 we mu/ rememb] h[ completely helpless we previ\sly 7 9 ! /range puzzles (f]$ ev5 by ! simple/ ( all spectra1 t ( hydrog54 ,,*apt] ,,vi ,,v>i\s ,,applications ,,( ,,! ,,bohr ,,!ory ,introduction4 ,we h dwelt at l5g? ^u ! !ory ( ! hydrog5 spectrum because x 0 p>ticul>ly 9 ?is relatively simple spectrum t ! ,bohr !ory fir/ %[$ its f]tility4 ,moreov]1 by /udy+ ! case ( ! hydrog5 atom ) its "o electron1 x is easi] to ga9 insight into ! fundam5tal ideas ( ! ,bohr !ory & its revolution>y "*4 ,naturally1 ! !ory is limit$ nei!r to ! hydrog5 atom nor to spectral ph5om5a1 b has a mu* m g5]al application4 ,z has already be5 said1 x takes1 z its problem1 ! explanation ( e "o ( ! physical & *emical prop]ties ( all ! elem5ts1 ) ! exception ( ^? prop]ties kn[n to be nucle> 7cf4 p4 #id74 ,?is v compreh5sive problem c naturally1 ev5 9 its ma9 outl9es1 be solv$ b gradually & by ! co-op]ation ( _m sci5ti/s1 & x is q impossible to g v deeply into ! great "w :i* has already be5 accompli%$1 & into ! difficulties :i* ,bohr & ! o!rs work+ on ! problem h ov]come4 ,we mu/ be cont5t ) %[+ "s especially significant features4 ,diff]5t ,emission ,spectra4 ,:ile ! neutral hydrog5 atom consi/s simply ( a positive nucleus & "o electron revolv+ ab\t ! nucleus1 ! o!r elem5ts1 9 ! neutral /ate1 h f two up to #ib electrons 9 ! sy/em ( electrons revolv+ ar\nd ! nucleus4 ,ev5 #b electrons1 z 9 ! helium atom1 make ! situation f> m complicat$1 s9ce we h 9 ?is case a sy/em ( #c bodies :i* mutually attract or repel ea* o!r4 ,we are ?us confront$ ) :at1 9 a/ronomy1 is kn[n z ! ?ree-body problem1 a problem consid]$ ) respect by all ma!maticians on acc\nt ( its difficulties4 ,9 a/ronomy1 ! difficulties are re/rict$ v mu* :5 ! mass ( "o body is _m times great] ?an t ( ! o!rs1 z 9 ! case ( ! mass ( ! sun 9 relation to t ( ! o!r planets4 ,"h1 by comp>atively simple me?ods1 x is possible to calculate ! motions inside a f9ite "t-int]val ) a high degree ( approximation ev5 :5 !re are n two b _m planets involv$4 ,we might n[ be tempt$ to believe t 9 ! atom we _h to deal ) comp>atively simple sy/ems--sol> sy/ems on small scale--s9ce ! mass ( ! nucelus is _m times great] ?an t ( ! electrons4 ,b ev5 if ! sugge/$ comp>ison illu/rates ! position ( ! nucleus z ! c5tral body :i* holds ! electrons toge!r by its p[] ( attraction1 ! comp>ison 9 o!r respects is mislead+4 ,:ile ! orbits ( ! planets 9 ! sol> sy/em may be at any di/ance :atsoev] f ! sun1 & ! motions ( ! planets are ev]y:]e gov]n$ by ! laws ( me*anics1 ! atomic processes1 accord+ to ! ,bohr !ory1 are *>act]iz$ by c]ta9 /ation>y /ates1 & only 9 ^! c ! laws ( me*anics possibly be appli$4 ,b 9 addition1 ! =ces betwe5 nucleus & electrons are det]m9$ n at all by ! masses1 b r by ! electric *>ges4 ,9 ! helium atom ! nucle> *>ge is only d\ble t ( an electron1 & ! attraction ( ! nucleus = an electron w !re=e be only twice z l>ge z ! repulsions betwe5 two electrons at ! same di/ance ap>t4 ,?is repulsion "u ^! circum/ances w1 !re=e1 also h great influ5ce on ! ensu+ motion4 ,9 elem5ts ) high] atomic numb]s ! nucle> *>ge has great] pr$om9ance ov] ! electron *>ges2 b1 on ! o!r h&1 !re are !n m electrons4 ,! situation is 9 ea* case m complicat$ ?an 9 ! hydrog5 atom4 ,nev]!less1 ! l9e spectra ( ! elem5ts ( high] atomic numb] %[ h[ ! l9es1 z 9 ! hydrog5 spectrum1 are arrang$ 9 s]ies al?\gh 9 a m complicat$ mann] 7cf4 p4 #ei72 9 any case 9 _m in/ances !re is great simil>ity betwe5 ! radiation f ! hydrog5 atom & t f ! m complicat$ atoms4 ,?us 9 ! l9e spectra ( _m elem5ts1 j z 9 t ( hydrog51 ! frequ5cy ( e l9e c be express$ z a diff]5ce betwe5 two t]ms1 involv+ c]ta9 integ]s :i* c pass ?r\gh a s]ies ( values4 ,f ! comb9ations ( t]ms1 two at a "t1 ! values ( correspond+ to ! diff]5t spectral l9es c be d]iv$4 ,?is s-call$ comb9ation pr9ciple enunciat$ by ! ,swiss physici/1 ,ritz1 c evid5tly be directly int]pret$ on ! basis ( ,bohr's po/ulates1 s9ce ! diff]5t comb9ations may be assum$ to correspond to def9ite atomic processes1 9 :i* !re is a transition betwe5 two /ation>y /ates1 ea* ( :i* corresponds to a spectral t]m4 ,moreov]1 ! t]ms 7cf4 p4 #ei7 may (t5 be approximately giv5 by ! ,rydb]g =mula ,k ---------- 7n 7 :]e ,k has ab\t ! same value z 9 hydrog51 & c take on a s]ies ( values 1 444 1 :ile n takes on integ] values4 ,s9ce we ?us det]m9e ! diff]5t l9es by assign+ values to ! two integ]s n & k 9 ea* t]m1 we h 9 ?is respect some?+ l ! f9e /ructure 9 ! hydrog5 spectrum1 :]e ! /ation>y /ates are det]m9$ by a pr9cipal quantum numb] & an auxili>y quantum numb]4 ,! spectra ( :i* we are speak+ "h1 & = :i* ! t]ms h ! =m giv5 above1 are (t5 call$ arc spectra1 because !y are emitt$ p>ticul>ly 9 ! light f ! electric arc or f ! vacuum tube4 ,we mu/ expect t ! simil>ity :i* exi/s 9 ! law = ! di/ribution ( spectral l9es w correspond to a simil>ity 9 ! atomic processes ( hydrog5 & ! o!r elem5ts4 ,! hydrog5 atom emits radiation correspond+ to ! diff]5t spectral l9es :5 an electron f an out] /ation>y orbit jumps1 ) a spr+ ( v>y+ size1 to an orbit ) l[] numb]1 & at la/ f9ds re/ 9 ! inn]mo/ orbit 9 a normal /ate1 :]e ! en]gy ( ! atom is z small z possible4 ,simil>ly1 we mu/ assume t ! electrons 9 o!r atoms1 dur+ processes ( radiation1 may proce$ 9 t[>ds ! nucleus until !y are collect$ z tightly z possible ab\t ! nucleus1 correspond+ to ! normal /ate ( ! atom1 :]e its en]gy cont5t is z small z possible3 8capture0 ( electrons by ! nucleus4 ,! region 9 space :i*1 9 ! normal /ate1 includes ! entire electron sy/em1 mu/ be assum$ to be ( ! same ord] ( magnitude z ! dim5sions ( ! atom & molecule :i* are d]iv$ f ! k9etic !ory ( gases4 ,?is normal /ate may be call$ a 8quiesc5t0 /ate1 s9ce ! atom _c emit radiation until x has be5 excit$ by ! introduction ( en]gy f )\t4 ,?is excitation process consi/s ( free+ "o 7or m7 electrons1 9 "s way or o!r1 f ! normal /ate & ei!r remov+ x out to a /ation>y orbit f>!r away f ! nucleus or eject+ x completely f ! atom4 ,n all electrons c be equally easily remov$ f ! quiesc5t /ate4 ,^? mov+ 9 small orbits ne> ! nucleus w be tight] b\nd ?an ^? mov+ 9 l>g] orbits f>!r f ! nucleus4 ,! arc spectrum is n[ caus$ by driv+ "o ( ! mo/ loosely b\nd electrons out into an orbit f>!r f ! nucleus or remov+ x completely f ! atom4 ,9 ! latt] case ! re/ ( ! atom1 :i* ) ! loss ( ! negative electron becomes a positive ion1 easily b9ds ano!r electron1 :i*1 ) ! emission ( radiation1 correspond+ to l9es ( ! s]ies spectrum1 c approa* clos] to ! nucleus4 ,let u n[ assume1 fir/1 t ?is radiat+ electron moves at s great a di/ance f ! nucleus & ! o!r electrons t ! entire inn] sy/em c be consid]$ z conc5trat$ 9 "o po9t2 !n ! situation is q z if we _h to deal ) a hydrog5 atom4 ,if ! atomic numb] is z high z #bi 7copp]71 = in/ance1 ! nucle> *>ge w consi/ ( tw5ty-n9e elem5t>y quanta ( positive electricity2 b s9ce !re are tw5ty-eight electrons 9 ! inn] sy/em1 ! resultant effect is t ( only "o elem5t>y quantum ( positive electricity1 z 9 ! case ( a hydrog5 nucleus4 ,! spectral l9es :i* are emitt$ 9 ! jumps betwe5 ! m di/ant pa?s w be practically ! same z hydrog5 l9es4 ,b1 s9ce 9 ! jumps betwe5 ^! di/ant orbits1 v small en]gy quanta w be emitt$1 ! frequ5cies are v small1 ! wave-l5g?s v great1 i4e41 ! l9es 9 "q lie f> out 9 ! infra-r$4 ,illu/ration3 ,,fig4 #bi4--;,diff]5t /ation>y orbits :i* ! out]mo/ 7#aa?7 electron ( sodium may describe4 ,:5 ! electron has come 9 s close to ! nucleus t ! di/ances 9 ! inn] sy/em _c be assum$ to be small 9 comp>ison to ! di/ance ( ! out] electron f ! nucleus1 ! situation is *ang$4 ,! =ce ) :i* ! nucleus & ! inn] electrons toge!r w "w ^u ! out] electron w be appreciably diff]5t f ! inv]se squ>e law ( attraction ( a po9t *>ge4 ,! consequ5ce ( ?is diff]5ce is t ! major axis 9 ! ellipse ( ! electron rotates sl[ly 9 ! plane ( ! orbit z describ$ 9 case ( ! !ory ( ! f9e /ructure ( ! hydrog5 l9es 7cf4 p4 #adf71 & ev5 if ! cause is diff]5t ! result is ! same2 ! orbit ( ! out] electron 9 ! /ation>y /ates w be *>act]iz$ by a quantum numb] n & an auxili>y quantum numb] k4 ,if ! electron comes /ill clos] to ! nucleus1 its motion is ev5 m complicat$4 ,:5 ! electron 9 its revolution is ne>e/ ! nucleus x w be able to dive into ! region ( ! inn] electrons1 & we c get motions l ^? %[n 9 ,fig4 #bi = "o ( ! elev5 sodium electrons4 ,! inn] dott$ circle is ! b\nd>y ( ! inn] sy/em :i* is giv5 by ! nucleus & ! t5 electrons rema9+ 9 ! 8quiesc5t0 /ate--little di/urb$ by ! re/less ,no4 #aa4 ,9 ! figure we c see great] or small] p>ts ( ,no4 #aa's diff]5t /ation>y orbits ) pr9cipal quantum numb]s #c & #d4 ,we %all n acc\nt fur!r = ! diff]5t orbits & ! spectral l9es produc$ by ! transitions betwe5 orbits1 b %all m]ely rem>k t ! yell[ sodium l9e1 :i* corresponds to ! ,fraunh(] ,d-l9e 7cf4 p4 #di71 is produc$ by ! transition #c-c1 betwe5 two orbits ) ! same pr9cipal quantum numb]4 ,! sket* %[s to a c]ta9 degree h[ fully _m details ( ! atomic processes c already be expla9$4 ,! !ory c ev5 give a natural explanation ( :y ! ,d-l9e is d\ble4 ,we h re/rict$ ourselves to ! case :]e only "o electron is remov$ f ! normal /ate ( ! neutral atom4 ,x may1 h[ev]1 happ5 t two electrons are eject$ f ! atom s t x becomes a positive ion ) two *>ges4 ,:5 an electron f ! outside is approa*+ ?is d\bly *>g$ ion x w1 at a di/ance1 be act$ ^u z if ! ion 7 a helium nucleus ) two positive *>ges4 ,! situation1 9 o!r words1 w be z 9 ! case ( ! false hydrog5 spectrum 7cf4 p4 #adb71 :]e ! con/ant ,k 9 ! =mula = ! hydrog5 spectrum is replac$ by ano!r :i* is v close to #d,k4 ,b if ! atom is n "o ( helium1 b "o ) a high] atomic numb]1 ! /ation>y orbits ( ! out] electron :i* approa* closely to ! nucleus w n co9cide exactly ) ^? 9 ! ioniz$ helium atom1 correspond+ to ! fact t ! t]ms 9 ! =mula = ! spectrum1 in/ead ( ! simple =m #d,k_/n1 h ! m complicat$ =m #d,k_/7n 74 ,spectra ( ?is nature are (t5 call$ sp>k spectra1 s9ce !y appe> especially /rong 9 electric sp>ks2 !y appe> also 9 light f vacuum tubes1 :5 an int]ruptor is plac$ 9 ! circuit1 mak+ ! dis*>ge int]mitt5t & m int5se4 ,an atom ) sev]al electrons c1 h[ev]1 be mu* m viol5tly excit$ f its quiesc5t /ate :5 an electron 9 ! inn] region ( ! atom is eject$ by a swiftly mov+ electron 7a ca?ode ray p>ticle or a -p>ticle f radium7 :i* travels ?r\gh ! atom4 ,su* an invasion produces a s]i\s di/urbance 9 ! /ability ( ! electron sy/em2 a recon/ruction foll[s1 9 :i* "o ( ! out]1 m loosely b\nd electrons takes ! vacant position4 ,9 ! transitions1 9 :i* ^! out] electrons come 91 r l>ge en]gy quanta are emitt$4 ,! emitt$ radiation has !re=e a v high frequ5cy2 mono*romatic ,x-rays are ?us emitt$4 ,s9ce ^! h _! orig9 9 processes f> )9 ! atom1 x c be und]/ood t ! diff]5t elem5ts h diff]5t *>act]i/ic ,x-ray spectra1 :i* c give v valuable in=mation ab\t ! /ructure ( ! electron sy/em 7cf4 p4 #ia74 ,betwe5 ^! ,x-ray spectra & ! s]ies spectra previ\sly m5tion$ !re lie1 z connect+ l9ks1 ^? spectra :i* are produc$ :5 electrons are eject$ f a gr\p 9 ! atom :i* does n belong to ! inn]mo/ gr\p1 b does n1 on ! o!r h&1 belong 9 ! out]mo/ gr\p 9 ! normal atom4 ,we h v little exp]im5tal k ab\t su* spectra1 because ! spectral l9es involv$ h wave-l5g?s ly+ betwe5 ab\t #ae & #ajj 4 ,rays ) ^! wave-l5g?s are absorb$ v easily by all possible sub/ances2 !y h v little effect on photographic plates1 :]e !y are absorb$ by ! gelat9e coat+ be=e !y h an opportunity to influ5ce ! molecules susceptible to light4 ,b !re c be sc>cely any d\bt t1 9 ! c\rse ( a few ye>s1 exp]im5tal te*nique w h rea*$ su* effici5cy t ?is doma9 ( ! spectrum1 s important = ! atomic !ory1 w also become accessible to exp]im5t4 ,9 individual cases1 wave-l5g?s z small z #bj h already be5 obta9$ by ,millikan4 ,( entirely diff]5t "* f ^! spectra are ! b& spectra4 ,!y are 9 g5]al produc$ by electric dis*>ges ?r\gh gases :i* are n v highly att5uat$ 7cf4 p4 #ee72 !y are n due to purely atomic processes1 b c be designat$ z molecul> spectra4 ,_! special "* is due to motions 9 ! molecule1 n only motions ( ! electrons1 b also oscillations & rotations ( ! nuclei ab\t ea* o!r4 ,we %all n g into ^! problems "h2 9 :at foll[s we %all inve/igate a c]ta9 type ( b& spectra some:at m closely 9 connection ) ! absorption ( radiation4 ,:ile ! b& spectra ) a spectroscope ( high resolv+ p[] c be m or less completely resolv$ into l9es1 ?is is n ! case ) ! cont9u\s spectra4 ,!y are emitt$ n only by gl[+ solids 7cf4 p4 #ed71 b also by _m gase\s sub/ances4 ,:5 su* gases are expos$ to electric dis*>ges !y emit1 9 addition to ! l9e spectra & b& spectra1 cont9u\s spectra :i* 9 c]ta9 p>ts ( ! spectrum furni% a backgr\nd = bright l9es :i* come out m /rongly4 ,x might seem impossible to correlate ^! ) ! ,bohr !ory2 b 9 reality a spectrum does n always h to consi/ ( %>p l9es4 ,?is c at once be se5 f ! correspond5ce pr9ciple4 ,if ! motions 9 ! /ation>y /ates are ( su* nature t !y c be resolv$ into a numb] ( discrete h>monic oscillations ea* ) its own p]iod 7= in/ance ! orbit ( an electron 9 a rotat+ ellipse2 cf4 p4 #adi71 !n1 accord+ to ! correspond5ce pr9ciple1 9 ! transition betwe5 two su* /ation>y /ates !re are produc$ %>p spectral l9es 8correspond+0 to ^! h>monic compon5ts4 ,b n all motions ( atomic sy/ems c be ?us resolv$ into a numb] ( def9ite h>monic oscillations4 ,:5 ?is _c be done1 ! /ation>y /ates _c be expect$ to be su* t transitions betwe5 !m produce radiation :i* c be resolv$ into %>p l9es4 ,a simple example1 :]e x is easily intelligible t ! ,bohr !ory w n lead to %>p l9es1 is obta9$ 9 a simple consid]ation ( ! hydrog5 atom4 ,let u exam9e ! l9es belong+ to ! ,balm] s]ies :i* are produc$ :5 an electron passes to ! ,no4 #b orbit f an orbit ) high] orbit numb]1 :i* is f>!r f ! nucleus4 ,z has be5 said1 we obta9 "h an upp] limit = ! frequ5cy correspond+ to a value ( ! out] orbit numb] :i* is inf9ite2 ?is means1 9 reality1 t ! electron 9 "o jump comes 9 f a di/ance s great t ! attraction ( ! nucleus is inf9itely small4 ,! en]gy releas$ by su* a jump is ! same z ! ioniz+ en]gy ,a :i* is requir$ to eject ! electron f ! orbit ,no4 #b & drive x f ! atom4 ,x is "h assum$1 h[ev]1 t ! electron out 9 ! di/ance 0 practically at re/4 ,if ! captur$ electron has a c]ta9 initial velocity outside1 x w h a correspond+ k9etic en]gy ,a4 ,:5 9 "o jump ?is electron comes f ! outside into orbit ,no4 #b1 ! en]gy lo/ by ! electron & emitt$ 9 ! =m ( radiation w be ! sum ( ! ioniz+ en]gy ,a & ! orig9al k9etic en]gy ,a4 ,! frequ5cy w !n become great] ?an t correspond+ to ,a2 & s9ce ! velocity ( ! electron be=e x is captur$ is n re/rict$ to c]ta9 def9ite values1 nei!r is ! value ( 4 ,! radiation f a great quantity ( hydrog5 atoms :i* are b9d+ electrons 9 ?is way w1 9 ! spectrum1 n be conc5trat$ 9 c]ta9 l9es1 b w be di/ribut$ ov] a region 9 ! ultra-violet :i* lies outside ( ! limit calculat$ f ! ,balm] =mula2 /ill 9 a c]ta9 s5se ?is cont9u\s spectrum is correlat$ ) ! ,balm] s]ies4 ,9 ! spectra f c]ta9 />s !re has actually be5 discov]$ a cont9u\s spectrum1 :i* lies beyond ! limits ( ! ,balm] s]ies & may be said to cont9ue x4 ,also ! ,x-rays1 :i* are g5]ally us$ 9 m$ic9e1 h v>y+ frequ5cies2 ?is is caus$ by ! fact t "s ( ! electrons :i*1 9 an ,x-ray tube1 /rike ! atoms ( ! antica?ode & travel f> into x at a high spe$1 lose a "p or all ( _! velocity )\t eject+ inn] electrons4 ,! lo/ k9etic en]gy !n appe>s directly z radiation4 ,^! rem>ks ought to be suffici5t to %[ t ! radiation1 = in/ance1 f a gl[+ body1 :]e ! int]play ( atoms & molecules is v complicat$1 c give a cont9u\s spectrum4 ,electron ,collisions4 ,! excitation ( an atom 9 ! normal /ate 7cf4 p4 #aeg71 by :i* "o ( its electrons is remov$ to an out] /ation>y orbit1 may be caus$ by a =eign electron :i* /rikes ! atom4 ,a /udy ( collisions betwe5 atoms & free electrons is !re=e ( ! greate/ importance :5 inve/igat+ m closely ! conditions by :i* s]ies spectra are produc$4 ,^! inve/igations c be c>ri$ out by giv+ free electrons def9ite velocities by lett+ !m pass ?r\gh an electric field1 :]e ! 8diff]5ce ( pot5tial0 is kn[n 9 ! pa? trav]s$ by ! electrons4 ,:5 an electron moves ?r\gh a region ) a diff]5ce ( pot5tial ( "o volt 7! usual te*nical unit71 ! k9etic en]gy ( ! electron w be increas$ by a def9ite am\nt 7( #af #aj erg74 ,if its initial velocity is z]o1 its passage ?r\gh ?is field w make ! velocity #fjj km4 p] second2 if ! pot5tial diff]5ce 7 #d volts1 #i volts1 etc41 ! velocity obta9$ by ! electron w\ld be #b1 #c1 etc41 times l>g]4 ,= ! sake ( brevity we %all say t ! k9etic en]gy ( an electron is1 = in/ance1 #ae volts1 :5 we mean t ! k9etic en]gy is z great z w\ld be giv5 by a diff]5ce ( pot5tial ( #ae volts4 ,9 #aiac ! ,g]man physici/ ,franck began a s]ies ( exp]im5ts by me?ods :i* made x possible to regulate accurately ! velocity ( ! electrons1 & to det]m9e ! k9etic en]gy be=e & aft] collisions ) atoms4 ,he fir/ appli$ ! me?ods to m]cury vap\r1 :]e ! conditions are p>ticul>ly simple1 s9ce ! m]cury molecules consi/ ( only "o atom4 ,franck bomb>d$ m]cury vap\r ) electrons all ( :i* _h ! same velocity4 ,he !n %[$ t if ! k9etic en]gy ( ! electrons 0 less ?an #di volts ! collisions ) ! atoms 7 completely 8ela/ic10 i4e41 ! direction ( ! electron c\ld be *ang$ by ! collision1 b n its velocity4 ,if1 h[ev]1 ! velocity ( ! imp++ electrons 0 increas$ s mu* t x 0 some:at l>g] ?an #di volts1 !re 0 an abrupt *ange 9 ! situation1 s9ce _m ( ! collisions became completely inela/ic1 i4e41 ! collid+ electron lo/ its entire velocity & gave up its entire k9etic en]gy to ! atom4 ,if ! initial velocity 0 ev5 great]1 s t ! k9etic en]gy ( ! collid+ electron 0 #f volts1 = in/ance1 !n :5 ! collision took place !re w\ld always be lo/ a k9etic en]gy ( #di volts1 s9ce ! electrons w\ld ei!r pres]ve _! k9etic en]gy intact or h x r$uc$ to #aa volt 7cf4 ,fig4 #cj74 ,illu/ration3 ,,fig4 #cj4--,s*ematic draw+ ( ,franck's exp]im5t ) electron collisions4 ,g is a gl[+ metal wire :i* emits electrons4 ,if betwe5 ,g & ! wire net ,t !re is a diff]5ce ( pot5tial ( #f volts1 ! electrons w pass ?r\gh ! holes ( ! net ) great velocity out into ! space ,r1 :]e !re is m]cury vap\r4 a repres5ts a free electron ,f & a m]cury atom ,hg be=e ! collision1 :ile b repres5ts !m aft] ! collision2 ) ! collision ,f loses a k9etic en]gy correspond+ to #di volts2 at ! same "t a b\nd electron ,b 9 ! atom goes ov] to a l>g] /ation>y orbit4 ,?is rem>kable ph5om5on c be und]/ood f ! ,bohr !ory if we assume t to s5d ! mo/ loosely b\nd electron 9 ! m]cury atom out to ! ne>e/ out] /ation>y orbit !re is requir$ an en]gy ( #di volts1 s9ce 9 t case1 accord+ to ! fir/ po/ulate1 an en]gy ( less ?an ?is magnitude _c be absorb$ by ! atom4 ,! use ( ! ^w 8und]/&+0 mu/ "h be qualifi$2 if ! =ces :i* influ5ce ! free electron z x comes into ! electron sy/em ( ! m]cury atom are no o!r ?an ! usual repulsion f ! electrons & ! attraction f ! nucleus1 ! conduct ( ! collid+ electron c 9 no way be expla9$ by ! laws ( me*anics4 ,b :at happ5s is 9 agreem5t ) ! *>act]i/ic /ability ( ! /ation>y /ates1 & ,bohr _h prophesi$ h[ x w\ld happ54 ,curi\sly en\gh ,franck believ$ 9 ! beg9n+ t 8 exp]im5t disagre$ ) ! ,bohr !ory because he made ! mi/ake ( suppos+ t :at happ5$ 0 m]ely ionization1 i4e41 complete disruption ( a b\nd electron f a m]cury atom4 ,franck's exp]im5ts %[$1 moreov]1 t m]cury vap\r1 z soon z ! inela/ic collisions appe>$1 began to emit ultra-violet light ( a def9ite wave-l5g?1 namely1 #becg 4 ,! product ( ! frequ5cy ( ?is light & ,planck's con/ant h agrees exactly ) ! en]gy quantum possess$ by an electron :i* has pass$ a pot5tial diff]5ce ( #di volts2 b ?is also agrees ) :at might be expect$1 accord+ to ! ,bohr !ory1 f ! radiation ! remov$ electron w\ld emit ^u return+ to ! normal /ate4 ,! en]gy :i* is respectively absorb$ & emitt$ 9 ! two transitions mu/ be inde$ h4 ,s9ce an electron c n only be driv5 out to ! next /ation>y orbit1 b also to an ev5 m di/ant "o 7or entirely eject$7 & !nce c come 9 aga9 9 "o or m jumps1 x is evid5t t a f> m complicat$ situation may arise4 ,! ,franck exp]im5t1 :i* n[ has be5 ext5d$ to _m o!r elem5ts1 cle>ly gives extraord9>ily valuable in=mation 9 su* cases4 ,9 m]cury x has be5 f\nd t ! en]gy a free electron mu/ h 9 ord] to eject an electron f an atom & turn ! atom into a positive ion1 corresponds to a diff]5ce ( pot5tial ( #ajh volts1 a value :i* ,bohr _h pr$ict$4 ,at ! same "t t ,franck's exp]im5ts1 9 ?is respect & 9 o!rs1 h /r5g!n$ ! ,bohr !ory 9 ! mo/ satisfactory way1 !y h also advanc$ its developm5t v mu*4 ,inde$ x may be said t !y h be5 ( ! greate/ help 9 atomic rese>*4 ,ev5 if ! spectroscope has great] importance1 ! inve/igations on electron collisions make ! realities 9 ! ,bohr !ory accessible to /udy 9 a m direct & palpable mann]4 ,illu/ration3 ,,fig4 #ca4--,/ratification ( light 9 a vacuum tube4 ,! peculi>ities 9 ! electron collisions appe> mo/ cle>ly 9 an old & well-kn[n ph5om5on ( light1 namely1 ! /ratification ( ! light 9 a vacuum tube 7,fig4 #ca74 ,?is /ratification1 :i* previ\sly seem$ s incompreh5sible1 agrees exactly ) ! feature s fundam5tal 9 ! atomic !ory t a free electron _c give en]gy "u a c]ta9 quantum to an atom4 ,we c imag9e t1 9 ! non-illum9at$ c5tral space betwe5 ! bright /rata1 ! electrons ea* "t "u ! influ5ce ( ! out] electric field obta9 ! am\nt ( k9etic en]gy :i* mu/ s]ve to excite ! atoms ( ! att5uat$ vap\r4 ,z has be5 said 7p4 #afa71 electron collisions may cause ! emission ( *>act]i/ic ,x-rays2 b to produce !m v great en]gy is requir$4 ,!re=e ! electrons :i* are to produce ?is effect mu/ h an opportunity to pass freely ?r\gh a c]ta9 region "u ! influ5ce ( a proportionately /rong electric field 7) pot5tial ( f #ajjj to #ajj1jjj volts & m74 ,! electrons f9d su* a field 9 a highly exhau/$ ,x-ray tube1 :]e ! electrons "u /rong pot5tial are driv5 f ! ca?ode aga9/ ! antica?ode1 into :i* !y p5etrate deeply4 ,absorption4 ,9 ! exp]im5ts previ\sly describ$ x 0 ! electron collisions :i* furni%$ ! en]gy requir$ to excite ! atoms1 i4e41 to c>ry !m f ! normal /ate ov] into a /ation>y /ate ) great] en]gy4 ,?is 8excitation en]gy0 may1 h[ev]1 also be furni%$ to ! atoms 9 ! =m ( radiation en]gy2 we %all n[ exam9e ?is case m closely4 ,let u assume t to transf] an atom f ! normal /ate to ano!r /ation>y /ate1 or1 9 o!r words1 to transf] "o ( ! electrons to an out] /ation>y orbit1 a c]ta9 quantity ( en]gy ,e is dem&$2 !n ! radiation emitt$ by ! atom :5 x returns to ! normal /ate w h a frequ5cy dep5d+ ^u ! relation ,e h or ,e_/h1 :]e h1 z usual1 is ! ,planck con/ant4 ,b j z ! atom 9 ! transition f ! /ation>y /ate to ! normal /ate c emit radiation only ) ! def9ite frequ5cy 1 !n ! opposite transition c only be p]=m$ by absorption ( radiation ) ! same frequ5cy2 :5 ?is happ5s ! absorb$ radiation en]gy has exactly ! value ,eh4 ,?is reciprocity1 :i* may be consid]$ z a direct consequ5ce ( ! ,bohr po/ulates1 agrees ) :at has be5 said 7cf4 p4 #ej7 ab\t ! correspond5ce betwe5 ! l9es 9 ! l9e spectrum ( an elem5t & ! d>k absorption l9es ( t elem5t--e4g41 ! ,fraunh(] l9es 9 ! sol> spectrum4 ,let u exam9e1 z an example1 ! yell[ sodium l9e1 ! ,d-l9e4 ,light ) ! correspond+ frequ5cy1 #ebf #aj vibrations p] second1 is emitt$ by a sodium atom1 :5 ! loose/ b\nd electron goes ov] f a /ation>y orbit ) quantum numb]s #c to ! orbit #c1 :i* belongs to ! normal /ate ( ! sodium atom4 ,! transition 9 ! opposite direction1 #c to #c1 c take place "u absorption ( radiation only :5 9 ! light f "s o!r s\rce ( light1 :i* passes ! sodium atoms1 !re are f\nd rays ) ! frequ5cy #ebf #aj4 ,ev5 if !re is pres5t radiation en]gy ) "s o!r frequ5cy1 ! sodium atoms take no notice ( ?is en]gy2 !y absorb only rays ) ! frequ5cy /at$1 & e "t an atom absorbs en]gy f a ray ! en]gy tak5 is always an en]gy quantum ( ! magnitude h1 i4e4 ab\t #fed #aj #ebf #aj #cdd #aj ergs 7#a erg is ! unit ( en]gy us$ 9 ! det]m9ation ( h74 ,:5 !re are pres5t a l>ge numb] ( sodium atoms 7z1 = in/ance1 9 ! previ\sly m5tion$ common salt flame71 ! transition #c to #c c take place 9 "s atoms1 ! transition #c to #c 9 o!rs2 !re=e1 at ! same "t !re c be absorption & radiation ( ! light 9 "q4 ,:e!r absorption or radiation at any giv5 "t has ! upp] h& dep5ds ^u v>i\s conditions 7temp]ature1 etc474 ,= ! sake ( simplicity we h "h tacitly und]/ood t !re c be b "o def9ite transition 7f ! normal /ate7 correspond+ to ! assumption t ! sodium spectrum _h no o!r l9es ?an ! ,d-l9e4 ,9 reality ?is is n ! case1 & !re c equally occur absorption ( rays ) l>g] frequ5cies belong+ to o!r spectral l9es 9 ! sodium atom & correspond+ to o!r possible transitions betwe5 /ation>y /ates 9 ! sodium atom4 ,if ! temp]ature ( ! sodium vap\r is suffici5tly l[1 9 :i* case almo/ all ! atoms are 9 ! normal /ate1 x is evid5t t 9 ! absorption only ^? l9es w appe> :i* correspond to transitions f ! normal /ate1 & :i* !re=e =m only a "p ( all ! l9es ( ! sodium spectrum4 ,we ?us obta9 an explanation ( ! previ\sly enigmatical circum/ance t n all spectral l9es :i* c appe> 9 emission w be f\nd 9 absorption4 ,at ! same "t we get1 9 absorption exp]im5ts1 valuable in=mation ab\t ! /ructure ( ! atom beyond :at ! obs]vations 9 ! emission spectra are able to give4 ,int]e/+ ph5om5a may arise ow+ to ! fact t ! jumps betwe5 ! /ation>y /ates ( ! atom sometimes1 z we "k1 take place 9 s+le jumps1 sometimes 9 d\ble or multiple jumps1 s t ! int]m$iate /ation>y /ates are jump$ ov]4 ,!re is !n evid5tly a possibility t absorption c take place1 = in/ance1 ) a d\ble jump ( an electron1 :i* may lat] return to ! orig9al /ation>y orbit 9 two s+le jumps4 ,! absorb$ radiation en]gy w !n appe> 9 emission ) two frequ5cies :i* are entirely diff]5t f ! frequ5cy ( ! absorb$ rays 7?is latt] 9 ?is case w be ! sum ( ! o!r two74 ,:5 an elem5t is illum9at$ ) a c]ta9 k9d ( rays1 x c1 9 o!r words1 emit 9 return rays ( a diff]5t nature4 ,su* *anges ( frequ5cies h also be5 obs]v$ 9 exp]im5t2 !y conta91 9 pr9ciple1 an explanation ( ! *>act]i/ic ph5om5on call$ fluoresc5ce4 ,we %all n g fur!r into ?is problem1 b dwell = a "t on ! *>act]i/ic ph5om5on ( absorption :i* is kn[n z ! photoelectric effect4 ,9 ?is ph5om5on 7cf4 p4 #aaf7 a metal plate1 by illum9ation ) ultra-violet light1 is made to s5d out electrons ) velocities ! maximum value ( :i* is indep5d5t ( ! /r5g? ( ! illum9ation1 b dep5ds only on ! frequ5cy ( ! rays4 ,:at happ5s is t "s ( ! electrons 9 ! metal :i* o!rwise h1 z _! function1 ! conduction ( ! electric curr5t1 by absorb+ radiation en]gy1 free !mselves f ! metal & leave x ) a c]ta9 velocity4 ,! reason :y ! rays = mo/ metals mu/ be ultra-violet 7i4e4 h a high frequ5cy & consequ5tly correspond to a proportionately l>ge en]gy quantum7 dep5ds ^u ! fact t ! en]gy quantum absorb$ by ! electrons mu/ be l>ge en\gh to c>ry out ! "w ( free+ ! electrons4 ,b z long z ! frequ5cy ( ! rays 7& !re=e _! en]gy quantum7 is no less ?an :at is ne$$ = ! free+ process1 x does n ne$ to h c]ta9 fix$ values4 ,if ! en]gy quantum h :i* ! rays c give (f is great] ?an is requir$ to free ! electrons1 ! surplus becomes k9etic en]gy 9 ! electrons1 :i* ?us acquire a velocity :i* is ! great] ! great] ! frequ5cy 1 & :i* co9cides ) ! maximum velocity obs]v$ 9 ! exp]im5ts4 ,:at happ5s "h is evid5tly some?+ :i* c be consid]$ z ! rev]se ( ! process :i* leads to ! production ( ! cont9u\s hydrog5 spectrum 7describ$ on p4 #afc74 ,9 ! latt] case1 electrons ) diff]5t velocities are b\nd by ! hydrog5 atoms1 :i* ?us emit rays ) frequ5cies increas+ ) increas+ velocity1 :ile1 vice v]sa1 9 ! photoelectric effect rays ) diff]5t frequ5cies free ! electrons & give !m velocities increas+ ) increas+ frequ5cies4 ,x mu/ be ackn[l$g$ t !re is some?+ v curi\s 9 ?is effect4 ,if ! electromagnetic waves1 z has be5 assum$1 are di/ribut$ ev5ly ov] ! field ( radiation1 x is n easy to und]/& :y !y give en]gy to "s atoms & n to o!rs1 & :y ! select$ ones always--) a giv5 frequ5cy--acquire a def9ite en]gy quantum1 indep5d5t ( ! int5sity ( ! radiation4 ,= small int5sities ( ! incid5t radiation1 ! atom1 9 ord] to acquire ! prop] quantum1 mu/ absorb en]gy f a great] "p ( ! field ( radiation 7or = a long] "t7 ?an = l>ge int5sities4 ,:5 ! atoms acquire en]gy 9 electron collisions1 ! situation is app>5tly easi] to und]/&1 s9ce 9 ?is case ! collid+ electrons give _! k9etic en]gy to def9ite atoms1 namely1 ^? :i* !y /rike4 ,e9/e91 9 #aije1 :5 !re 0 n yet any talk ( ! nucle> atom or ! ,bohr !ory1 enunciat$ 8 !ory ( light quanta1 accord+ to :i* ! en]gy ( radiation is n only emitt$ & absorb$ by ! atoms 9 c]ta9 quanta1 ) magnitudes det]m9$ by ! frequ5cy 1 b is also pres5t 9 ! field ( radiation 9 su* quanta4 ,:5 an atom emits an en]gy quantum h1 ?is en]gy w n spread out 9 waves on all sides1 b w travel 9 a def9ite direction--l a little lump ( en]gy1 we might say4 ,^! light quanta1 z !y are call$1 c1 l ! electrons1 hit c]ta9 atoms4 ,b ev5 if 9 ?is !ory ! difficulties m5tion$ are1 app>5tly1 ov]come1 f> great] difficulties are introduc$2 inde$ x may be said t ! :ole wave !ory becomes %r\d$ 9 d>kness4 ,! v numb] :i* *>act]izes ! diff]5t k9ds ( rays loses its significance z a frequ5cy & ! ph5om5a ( int]f]5ce--reflection1 disp]sion1 diffraction1 & s on--:i* are s fundam5tal 9 ! wave !ory ( ! propagation ( light1 & on :i*1 = in/ance1 ! me*anism ( ! human eye is bas$1 receive no explanation 9 ! !ory ( light quanta4 ,= in/ance1 9 ord] to und]/& t grat+ spectra c be produc$ at all1 we mu/ ?9k ( a co-op]ation ( ! light f all ! rul+s 7cf4 ,fig4 #aj1 p4 #dg71 & ?is co-op]ation _c arise if all ! slits at a giv5 mom5t d n receive light emitt$ f ! same atom4 ,9 a bundle ( rays :i* comes 9 at "r angles to a grat+1 we mu/1 9 ord] to expla9 ! int]f]5ce1 assume t ! /ate ( oscillation at a giv5 mom5t is ! same 9 all slits1 t1 = in/ance1 !re are wave cre/s 9 all at ! same "t1 if we borr[ a picture f ! repres5tation ( wat] waves4 ,only 9 ?is case !re c beh9d ! grat+ at c]ta9 fix$ places--= :i* ! diff]5ce 9 ! wave-l5g? ( ! di/ances f successive slits is a :ole numb] ( wave-l5g?s--/eadily come wave cre/s f all ! slits at "o mom5t & wave tr\ghs f all at ano!r mom5t 7! classical explanation ( ! 8me*anism0 ( a grat+74 ,if we imag9e1 h[ev]1 t "s slits are hit by light quanta f "o atom & o!rs f a second atom1 x is pure *ance if !re are wave cre/s simultane\sly 9 all slits1 because ! diff]5t atoms 9 a s\rce ( light emit light at diff]5t times1 dep5d+ purely on *ance4 ,an und]/&+ ( ! obs]v$ effect ( a grat+ on light seems !n out ( "q4 ,! !ory ( light quanta may ?us be comp>$ ) m$ic9e :i* w cause ! disease to vani% b kill ! pati5t4 ,:5 ,e9/e91 :o has made s _m ess5tial contributions 9 ! field ( ! quantum !ory1 advocat$ ^! rem>kable repres5tations ab\t ! propagation ( radiation en]gy he 0 naturally n bl9d to ! great difficulties j indicat$4 ,8 appreh5sion ( ! my/]i\s light 9 :i* ! ph5om5a ( int]f]5ce appe> on 8 !ory is %[n 9 ! fact t 9 8 consid]ations he introduces some?+ :i* he calls a 8gho/0 field ( radiation to help to acc\nt = ! obs]v$ facts4 ,b he has evid5tly wi%$ to foll[ ! p>adoxical 9 ! ph5om5a ( radiation out to ! end 9 ! hope ( mak+ "s advance 9 our k4 ,?is matt] is introduc$ "h because ! ,e9/e9 light quanta h play$ an important "p 9 discussions ab\t ! quantum !ory1 & "s read]s may h he>d ab\t !m )\t be+ cle> z to ! real /&+ ( ! !ory ( light quanta4 ,! fact mu/ be emphasiz$ t ?is !ory 9 no way has sprung f ! ,bohr !ory1 to say no?+ ( its be+ a necess>y consequ5ce ( x4 ,9 ! ,bohr !ory1 absorption & radiation mu/ be said to be completely reciprocal processes1 i4e4 processes ( ess5tially ! same nature1 b proce$+ 9 opposite directions4 ,9 itself x _c be said to be m incompreh5sible t an atom absorbs en]gy f a field ( radiation 9 agreem5t ) ! ,bohr po/ulates ?an t x emits en]gy into ! field2 b 9 bo? cases we naturally enc\nt] ! great difficulties m5tion$ 9 ,*ap4 ,v4 ,we h hi!rto re/rict$ ourselves to ! purely atomic processes4 ,b j z 9 ! emission ( radiation we meet spectra :i* owe _! *>act]i/ics to molecul> processes 7b& spectra1 cf4 p4 #afb71 we h also absorption spectra ) *>act]i/ics dep5d+ ess5tially ^u motions ( ! atomic nuclei 9 ! molecules4 ,a p>ticul>ly int]e/+ & in/ructive example ( ?is nature is met ) 9 ! infra-r$ region ( ! spectrum 9 c]ta9 broad absorption l9es or absorption b&s1 :i* are due to gases hav+ molecules conta9+ sev]al atoms4 ,9 hydrog5 *loride1 = in/ance1 !re is f\nd1 9 ! region ( ! spectrum :i* corresponds to a wave-l5g? ( ab\t #ce 1 su* an absorption b&1 :i* by m accurate inve/igation has be5 %[n to consi/ ( a great numb] ( absorption l9es4 ,! explanation ( ?is collection ( l9es mu/ be s\ght 9 ! motions :i* ! hydrog5 nucleus & ! *lor9e nucleus p]=m1 z !y 9 "p vibrate ) respect to ea* o!r & 9 "p rotate ab\t _! common c5tre ( gravity4 ,j z 9 ! case ( ! motions ( ! electrons 9 ! atom1 !re are also c]ta9 /ation>y /ates = ! nucle> motions4 ,:5 ! molecule absorbs radiation en]gy x w g f "o ( ^! /ates to ano!r1 :]e ! en]gy cont5t is great]4 ,?is absorption ( en]gy proce$s accord+ to ! quantum rule1 i4e41 ! product ( ! ,planck con/ant h & ! frequ5cy = ! absorb$ radiation mu/ be equal to ! diff]5ce 9 en]gy betwe5 ! two /ation>y /ates2 only ^? rays :i* h frequ5cies fulfill+ ?is condition are absorb$4 ,illu/ration3 ,,fig4 #cb4--,s*ematic repres5tation ( possible motions 9 a molecule ( hydrog5 *loride4 ,o is ! c5tre ( gravity ( ! molecule4 ,! black circles give ! /ates ( equilibrium ( ! nuclei1 ! circles s _! out] positions 9 oscillat+1 & ! circles r positions dur+ ! rotation ( ! nuclei4 ,9 hydrog5 *loride1 at /&>d temp]ature1 ! molecules w be 9 diff]5t /ation>y /ates ( rotation 7cf4 ! rem>ks on p4 #bg71 correspond+ to diff]5t def9ite values ( ! rotation frequ5cy1 :ile ! nuclei1 on ! o!r h&1 mu/ be assum$ to be at re/ ) ref]5ce to ea* o!r1 i4e41 !y pres]ve _! mutual di/ance4 ,9 ,fig4 #cb1 ,h & ,cl indicate ! circles :i* ! two nuclei w describe ab\t ! c5tre ( gravity2 "h1 h[ev]1 x mu/ be rem>k$ t ! hydrog5 circle is drawn too small 9 comp>ison ) t ( *lor9e4 ,if heat rays ) all possible wave-l5g?s ar\nd #ce are s5t ?r\gh ! hydrog5 *loride1 t radiation en]gy w be absorb$ :i* c 9 "p set ! nuclei 9 oscillation & 9 "p *ange ! /ate ( rotation4 ,let u = a mom5t assume t only ! =m] *ange c\ld happ54 ,!n a ray ) wave-l5g? #cdf w\ld be absorb$1 ?is frequ5cy correspond+ to ! en]gy 9 ! /ation>y /ate ( oscillation into :i* ! molecule goes2 ?is frequ5cy is v ne>ly equal to ! frequ5cy ) :i* ! nuclei vibrate relatively to ea* o!r4 ,9 reality1 at ! same "t t ! nucleus is set 9 oscillation1 !re w always be a *ange 9 ! /ate ( rotation--consi/+ ei!r 9 an increase or 9 a decrease 9 ! velocity ( rotation4 ,! en]gy absorb$1 & !re=e ! frequ5cy = ! radiation absorb$1 is !reby *ang$ a little1 s t 9 ! spectrum ( ! rays s5t ?r\gh we d n obta9 an absorption l9e correspond+ to #cdf 1 b a l9e some:at remov$ f t4 ,s9ce !re are1 h[ev]1 _m /ation>y /ates ( rotation to />t f1 & s9ce 9 "s molecules !re is "o transition1 9 o!rs ano!r1 we get _m absorption l9es on ea* side ( #cdf 4 ,ev5 be=e ,bohr prop\nd$ 8 !ory1 at a "t :5 ! quantum !ory did n yet h a cl>ifi$ =m1 ! ,dani% *emi/1 ,niels ,bj]rum1 _h pr$ict$ t ! infra-r$ absorption l9es ought to h su* a /ructure4 ,?is /ructure mu/ be int]pret$ 9 ! above way :i* diff]s some:at f ,bj]rum's ideas1 b 8 pr$iction 0 ess5tially /r5g!n$ by inve/igations1 & x 0 "o ( ! mo/ significant features 9 ! developm5t ( ! quantum !ory prior to #aiac4 ,! fir/ to detect ! /ructure ( ! infra-r$ absorption b&s 0 ! ,sw$i% physici/1 ,eva von ,bahr4 ,h] exp]im5ts 7 lat] ext5d$ 9 a mo/ significant way by ! "w ( ,imes & o!r ,am]ican inve/igators4 ,!y enable u to calculate exactly ! di/ance betwe5 ! two nuclei 9 ! molecule4 ,x may be ask$ :at becomes ( ! en]gy :i* ! hydrog5 *loride molecule ?us absorbs1 & :e!r x necess>ily aft] a long] or %ort] "t mu/ be re-emitt$ z radiation4 ,! latt] is n ! case4 ,9 a collision betwe5 molecules or atoms1 ! en]gy :i* "o molecule 7or atom7 has absorb$ by radiation c und\bt$ly be transf]r$ to ano!r molecule1 ! velocity ( :i* is !reby increas$4 ,! !oretical necessity ( ! occurr5ce ( su* collisions 0 cle>ly %[n = ! fir/ "t 9 a v significant inve/igation by two ( ,bohr's /ud5ts1 ,kle9 & ,rossel&4 ,)\t collisions ( ?is nature ! radiation en]gy absorb$ c\ld nev] be trans=m$ into heat en]gy4 ,"h we come to a v great & important field1 :i* has a v close connection ) ! !ory ( ! *emical processes & to a bett] explanation ( :i* ! m rec5t exp]im5ts ( ,franck & 8 co-work]s h made important contributions4 ,,*apt] ,,vii ,,! ,,/ructure ,,( ,,! ,,atom ,,& ,,! ,,*emical ,,prop]ties ,,( ,,! ,,elem5ts ,introduction4 ,we h hi!rto re/rict$ ourselves ma9ly to ^? applications ( ! ,bohr !ory :i* h a direct connection ) ! processes ( radiation4 ,we h %[n h[ f]tile ! !ory has prov$ to be1 h[ _m problems1 previ\sly inexplicable1 h be5 solv$1 & :at exact agreem5t has be5 e/abli%$ betwe5 exp]im5t & !ory 9 ?is compreh5sive field4 ,we may n[ ask h[ ! !ory acc\nts = ! *emical behavi\r ( ! diff]5t elem5ts4 ,z e>ly z #aiac1 ,bohr1 9 connection ) 8 rese>*es on spectral ph5om5a1 _h consid]$ ! *emical prop]ties ( ! elem5ts & _h po9t$ out int]e/+ possibilities4 ,illu/ration3 ,,fig4 #cc4--;,e>ly repres5tation ( ! =mation ( a hydrog5 molecule 7,bohr1 #aiac74 ,! ,comb9ation ( ,atoms into ,molecules4 ,9 8 discussion ( hydrog51 ,bohr sugge/$ a model = ! /ructure ( its molecule1 :i* we %all give "h1 because1 by a simple example1 x illu/rates h[ two neutral atoms may =m a molecule 7cf4 p4 #ac74 ,9 ,fig4 #cc1 a1 ,k,e & ,k,e are two neutral hydrog5 atoms :i* are approa*+ ea* o!r ) ! orbits ( ! two electrons p>allel4 ,! nucleus ,k & ! electron ,e !n attract ea* o!r z d ! nucleus ,k & ! electron ,e4 ,! two electrons repel ea* o!r z d ! two nuclei2 b :5 ! electrons are 9 opposite positions ( _! orbits1 ! =ces ( attraction outweigh ! effect ( ! =ces ( repulsion4 ,calculation %[s t :5 ! atoms are all[$ to approa* ea* o!r ! positions ( ! atoms w be z is %[n 9 ,fig4 #cc1 b1 :]e ! orbits are clos] to ea* o!r ?an ! nuclei4 ,f9ally1 = small di/ances ( ! two nuclei1 ! two orbits w be m]g$ into "o1 z is %[n 9 ,fig4 #cc1 c4 ,?is orbit w be slightly l>g] ?an ! orig9al ones4 ,! two hydrog5 atoms may1 9 ?is way1 comb9e into "o molecule4 ,9 fact1 an equilibrium position c be f\nd = :i* ! nuclei are held toge!r1 9 spite ( _! mutual repulsion1 by ! attractive =ces exi/+ betwe5 !m & ! electrons :i* are mov+ 9 _! common orbit4 ,x mu/1 h[ev]1 be assum$1 = reasons :i* _c be giv5 "h1 t ! hydrog5 molecule is1 9 reality1 con/ruct$ some:at diff]5tly2 probably ! orbits ( ! electrons make an angle ) ea* o!r4 ,! =mation ( a hydrog5 molecule may also be suppos$ to occur :5 a positive hydrog5 ion1 i4e41 a hydrog5 nucleus1 & a negative hydrog5 ion1 i4e41 a hydrog5 nucleus ) two electrons1 are drawn toge!r by _! mutual attractions4 ,! =ces ( attraction w\ld be mu* /rong] ?an 9 ! fir/ example giv51 & ! =mation ( a neutral molecule w\ld n take place 9 ! same way4 ,m en]gy w\ld also be releas$1 b ! f9al result w be ! same4 ,j z 9 ! case ( ! hydrog5 molecule1 o!r molecules may be =m$ f atoms belong+ to ! same or to diff]5t elem5ts4 ,! me?od ( =mation ( molecules v>ies accord+ z x is a union ( neutral molecules 9 ! normal /ate1 or a union ( positive & negative ions4 ,conv]sely1 by *emical decomposition a molecule c be sep>at$ ei!r into neutral p>ts or into ions4 ,if1 = in/ance1 common salt 7sodium *loride1 ,na,cl7 is dissolv$ 9 wat]1 ! salt molecules are1 "u ! influ5ce ( ! wat] molecules1 decompos$ 9 ,na-ions ) "o positive *>ge & ,cl-ions ) "o negative *>ge1 correspond+ to ! monoval5t electropositive "* ( sodium & ! monoval5t electronegative "* ( *lor9e4 ,! possibilities are1 h[ev]1 f> f be+ exhau/$ by ^! two me?ods ( composition & decomposition4 ,an atom may exi/ n only 9 ! normal /ate :]e x has its complete numb] ( electrons collect$ z tightly z possible ab\t ! nucleus1 & 9 ! ioniz$ /ate ) "o or m too _m or too few electrons2 b 9 a neutral atom "o or m ( ! out] electrons may be 9 a /ation>y orbit at a great] di/ance f ! nucleus ?an corresponds to ! normal /ation>y /ate4 ,x is easy to und]/& t an atom 9 su* an 8excit$0 or 7z x is call$ 9 *emi/ry7 active /ate (t5 f9ds x easi] to act 9 conc]t ) o!r atoms ?an :5 x is 9 ! normal /ate2 9 ?is latt] /ate ! atom is (t5 m l a little compact lump ( neutral sub/ance ?an 9 ! active /ate4 ,x w1 9 any case1 be und]/ood t ! int]play betwe5 ! atoms1 :i* reveals itself 9 ! *emical processes or reactions betwe5 diff]5t elem5ts1 (f]s _m opportunities = ! ,bohr !ory to give 9 ! future a m detail$ explanation ?an 0 possible to ! e>li] !ories ( *emi/ry4 ,we mu/ also m5tion ! fact t x has become possible to elucidate 9 ma9 features ! ph5om5a1 hi!rto unexpla9$1 ( ! *emical effects ( light1 z on a photographic plate 7photo*emi/ry7 & ( catalysis1 :i* consi/s 9 br++ ab\t1 or accel]at+1 ! *emical int]action betwe5 two sub/ances by ! pres5ce ( a ?ird sub/ance :i* does n itself ent] 9 ! comp\nd1 & (t5 ne$s only to be pres5t 9 v small quantities4 ,x mu/1 h[ev]1 be emphasiz$ t at pres5t we d n yet possess a detail$ !ory ( molecul> con/itution comp>able ) our k ( ! /ructure ( ! atoms4 ,! ,p]iodic ,sy/em4 ,in/ead ( inquir+ h[ ! *emical processes may take place1 we %all n[ /udy ! g5]al correlation betwe5 ! *emical prop]ties & ! atomic numb]s ( ! elem5ts1 a correlation :i* has f\nd its empirical expression 9 ! natural or p]iodic sy/em ( ! elem5ts 7cf4 p4 #bc74 ,! explanation ( ! puzzles ( ?is sy/em mu/ be said to be "o ( ! f9e/ results :i* ,bohr has obta9$1 & x con/itutes a /rik+ evid5ce 9 fav\r ( ! quantum !ory ( atoms4 ,!re is no?+ new 9 ! idea ( connect+ ! arrangem5t ( ! elem5ts 9 ! p]iodic sy/em ) an arrangem5t ( p>ticles 9 ! atom 9 regul> gr\ps1 ! "* ( :i* v>ies1 s to say1 p]iodically ) increas+ numb] ( p>ticles4 ,9 ! atom model ( ,"l ,kelv9 & ,j4 ,j4 ,?omson 7cf4 p4 #hf71 ) ! positive electricity di/ribut$ ov] ! volume ( ! :ole atom1 ,?omson tri$ to expla9 c]ta9 lead+ *>act]i/ics ( ! p]iodic sy/em by imag9+ ! electrons z arrang$ 9 sev]al circul> r+s ab\t ! c5tre ( ! atom4 ,he po9t$ out t ! /ability ( ! electronic configurations ( ?is type v>i$ 9 a rem>kable p]iodic way ) ! numb] ( electrons 9 ! atom4 ,by consid]ations ( ?is nature ,?omson 0 able to enunciate a s]ies ( analogies to ! behavi\r ( ! elem5ts 9 ! p]iodic sy/em z reg>ds ! t5d5cy ( ! neutral atoms to lose "o or m electrons 7electropositive elem5ts7 or to take up "o or m electrons 7electronegative elem5ts74 ,b1 sett+ aside possible objections to 8 consid]ations & calculations1 ! connection ) ! sy/em 0 v loose & g5]al1 & 8 !ory lo/ its fundam5tal support :5 8 atomic model _h to give way to ,ru!r=d's4 ,) ,bohr's !ory ! dem& = a /able sy/em ( electrons 0 plac$ 9 an entirely new light4 ,9 8 treatise ( #aiac1 ,bohr tri$ to give an explanation ( ! /ructure ( ! atom1 by ?9k+ ( ! electrons z mov+ 9 a l>g] or small] numb] ( circul> r+s ab\t ! nucleus4 ,8 !ory did n exclude ! possibility ( orbits ( electrons hav+ diff]5t directions 9 space in/ead ( ly+ 9 "o plane or be+ p>allel4 ,! t5d5cy ( ! consid]ations 0 to atta9 a def9ite1 unique det]m9ation ( ! /ructure ( ! atom1 z is dem&$ by ! pron\nc$ /ability ( ! *emical & physical prop]ties ( ! elem5ts4 ,! results 71 h[ev]1 r unsatisfactory1 & x became m & m cle> t ! bases ( ! quantum !ory 7 n suffici5tly develop$ to lead 9 an unambigu\s way to a def9ite picture ( ! atom4 ,n[adays ! simple conception ( ! electrons mov+ 9 circul> r+s 9 ! field ( ! nucleus is def9itely ab&on$1 & replac$ by a picture ( atomic con/itution ( :i* we %all speak pres5tly4 ,9 ! foll[+ ye>s ! g5]al conception ( ! gr\p di/ribution ( ! electrons 9 ! atom =m$ ! basis ( _m !oretical inve/igations1 :i* 9 v>i\s respects h l$ to a clos] und]/&+ ( *emical & physical facts4 ,! ,g]man physici/1 ,kossel1 %[$ t ! *>act]i/ic ,x-ray spectra ( ! elem5ts1 :i* are due to a process ( recon/ruction ( ! atom subsequ5t to ! removal ( "o or m ( ! inn]mo/ electrons 7cf4 p4 #afa71 give a mo/ /rik+ support to ! assumption t ! electrons are di/ribut$ 9 diff]5t gr\ps 9 :i* !y are b\nd ) diff]5t /r5g? to ! atom4 ,! connection betwe5 ! electron gr\ps & ! *emical val5ce prop]ties ( ! atoms1 to :i* ,?omson _h fir/ drawn att5tion & :i* also play$ an important "p 9 ,bohr's e>ly consid]ations1 0 fur!r develop$ 9 a significant way by ,kossel1 z well z by ,lewis & by ,langmuir 9 ,am]ica4 ,^! *emical !ories _h1 h[ev]1 little or no connection ) ! quantum !ory ( atomic processes2 ev5 ! special features ( ! ,ru!r=d atom1 :i* are ( ess5tial importance 9 ! !ory ( ! hydrog5 spectrum & ( o!r spectra1 play$ only a subord9ate "p4 ,9 #aibj ,bohr %[$ h[1 by ! developm5t ( ! quantum !ory :i* _h tak5 place 9 ! meantime1 & ! ma9 features ( :i* consi/$ 9 ! introduction ( m ?an "o quantum numb] = ! det]m9ation ( ! /ation>y /ates & 9 ! e/abli%m5t ( ! correspond5ce pr9ciple1 ! problem ( ! /ructure ( ! atom _h appe>$ 9 a new light4 ,9 fact1 he outl9$ a g5]al picture ( atomic con/itution1 bas$ on ! quantum !ory1 :i* 9 a rem>kable way acc\nt$ = ! prop]ties ( ! elem5ts4 ,9 ord] to decide d\btful que/ions1 he has (t5 _h to call to 8 aid ! obs]v$ prop]ties ( elem5ts1 & x mu/ be readily admitt$ t ! f9i%+ t\*es ( ! !ory are /ill lack+4 ,b f 8 g5]al />t+-po9t he has be5 able to outl9e ! ar*itecture ( ev5 ! mo/ complex atomic /ructures & to expla91 n only ! kn[n regul>ities1 b also ! app>5t irregul>ities ( ! p]iodic sy/em ( ! elem5ts4 ,! me?od ,bohr us$ 9 8 attempt to solve ! problem 0 to /udy h[ a neutral normal atom may gradually be =m$ by ! successive captur+ & b9d+ ( ! individual electrons 9 ! field ( =ce ab\t ! nucleus ( ! atom4 ,he began by assum+ t he _h a solit>y nucleus ) a positive *>ge ( a giv5 magnitude4 ,to ?is nucleus free electrons are n[ add$1 "o aft] ! o!r1 until ! nucleus has tak5 on ! numb] suffici5t to neutralize ! nucle> *>ge4 ,ea* individual electron und]goes a 8b9d+0 process1 i4e4 x c move 9 diff]5t possible /ation>y orbits ab\t ! nucleus & ! electrons already b\nd4 ,) ! emission ( radiation x c g f /ation>y /ates ) great] en]gy to o!rs ) less en]gy1 end+ its j\rney by rema9+ 9 ! orbit :i* corresponds to ! lea/ possible en]gy4 ,we may designate ?is /ate ( lea/ en]gy z ! normal /ate ( ! sy/em1 :i*1 h[ev]1 is only a positive atomic ion1 s long z all ! electrons ne$$ = neutralization are n yet captur$4 ,f ! exposition 9 ! prec$+ *apt] x w be se5 t ! ord9>y s]ies spectra 7arc spectra7 may be consid]$ z correspond+ to ! la/ /age 9 ?is =mation process1 s9ce ! emission ( ea* l9e 9 su* a spectrum is due to a transition betwe5 two /ation>y /ates 9 ea* ( :i* ,n-#a electrons are b\nd 9 _! normal /ate1 i4e4 z tight z possible1 by ! nucleus1 :ile ! ,n? electron moves 9 an orbit ma9ly outside ! region ( ! o!r electrons4 ,9 ! same way ! sp>k spectra give witness ( ! la/ /age b "o ( ! =mation process ( ! atom1 s9ce "h ,n-#b electrons are b\nd 9 _! normal /ate :ile an ,n-#a? electron moves 9 an orbit l>ge comp>$ ) ! dim5sions ( ! orbits ( ! inn] electrons4 ,f ^! rem>ks x w be cle> t ! /udy ( ! s]ies spectra is ( great importance = ! clos] inve/igation ( ! process ( =mation ( ! atom outl9$ above4 ,fur!rmore1 ! g5]al ideas ( ! correspond5ce pr9ciple1 :i* directly connects ! possibility ( transition f "o /ation>y /ate to ano!r ) ! motion ( ! electron1 has be5 v useful 9 ?r[+ light on ! individual captur+ processes & on ! /ability ( ! electronic configurations =m$ by ^!4 ,9 :at foll[s we _c1 h[ev]1 reproduce ,bohr's argum5ts at l5g?2 we mu/ satisfy ourselves ) "s h9ts "h & !re1 & = ! re/ re/rict ourselves to giv+ "s ( ! pr9cipal results4 ,be=e go+ f>!r we %all recall :at has previ\sly be5 said ab\t ! quantum numb]s4 ,9 ! undi/urb$ hydrog5 atom1 ! /ation>y orbits c be numb]$ ) ! pr9cipal quantum numb]s #a1 #b1 #c 444 n4 ,b to ea* pr9cipal quantum numb] !re corresponds n "o b sev]al /ates1 ea* ) its auxili>y quantum numb] #a1 #b1 #c 444 k1 k at ! mo/ be+ equal to ! pr9cipal quantum numb]4 ,9 a simil> way1 ! /ation>y orbits ( ! electrons 9 an atom conta9+ sev]al electrons c be indicat$ by two quantum numb]s1 ! #c orbit1 = in/ance1 be+ t ) pr9cipal quantum numb] #c & auxili>y quantum numb] #b4 ,b :ile 9 ! hydrog5 atom ! pr9cipal quantum numb] n1 9 ! /ation>y orbits :i* are sl[ly rotat+ ellipses1 is v simply connect$ ) ! l5g? ( ! major axis ( ! ellipse1 & k3 n is ! ratio betwe5 ! m9or & major axes1 /ill 9 o!r atoms ) complex sy/ems ( electrons ! significance ( ! pr9cipal quantum numb] is n s simple & ! orbit ( an electron consi/s ( a sequ5ce ( loops ( m complicat$ =m 7cf4 ,fig4 #bi74 ,we mu/ satisfy ourselves ) ! /atem5t t a def9ition ( _! significance c be giv51 b only by ma!matical-physical consid]ations :i* we _c ent] into "h4 ,x may1 h[ev]1 be /at$ t1 if we re/rict ourselves to a def9ite atom1 ! rule w hold t1 among a s]ies ( orbits ) ! same auxili>y quantum numb] b diff]5t pr9cipal quantum numb]s1 t orbit 9 :i* ! electron atta9s a great] di/ance f ! nucleus has ! high] numb]4 ,ano!r rule :i* holds is1 t an orbit ) a small auxili>y quantum numb] 9 comp>ison ) its pr9cipal quantum numb] 7z #d = in/ance1 cf4 ,fig4 #bi71 w consi/ ( v oblong loops ) a v great diff]5ce betwe5 ! greate/ & lea/ di/ances ( ! electron f ! nucleus1 :ile ! orbit w be a circle :5 ! two quantum numb]s are ! same z = #a1 #b1 #c4 ,al?\gh ea* orbit has two quantum numb]s1 we (t5 speak simply ( ! #a-1 #b-1 #c- 444 n-quantum orbits1 mean+ "h ! orbits ) ! pr9cipal quantum numb]s #a1 #b1 #c 444 n4 ,! "o electron ( hydrog5 w1 ^u be+ captur$1 fir/ be at 8re/0 :5 x rea*es ! #a-pa?1 & we might p]haps be l$ to expect t 9 ! atoms ) great] nucle> *>ges ! electrons 9 ! normal /ate also w\ld be 9 ! "o quantum orbit #a1 because to ?is corresponds ! lea/ en]gy 9 hydrog54 ,?is assumption =m$ actually ! basis ( ,bohr's "w ( #aiac on ! /ructure ( ! heavi] atoms4 ,x _c be ma9ta9$1 h[ev]4 ,consid]ations ( !oretical & empirical nature lead to ! assumption t ! electrons :i* already are ga!r$ ab\t ! nucleus c make room only to a c]ta9 ext5t = new ones1 mov+ 9 orbits ( ! same pr9cipal quantum numb]4 ,^? electrons :i* are captur$ lat] are kept at an appropriate di/ance2 !y are1 = in/ance1 prev5t$ f pass+ f a #c-quantum orbit to a #b-quantum "o1 if ! numb] ( electrons mov+ 9 #b-quantum orbits has rea*$ a c]ta9 maximum value4 ,:5 x is said t ! captur$ electrons end 9 ! /ation>y /ate :i* corresponds to ! lea/ en]gy1 x mu/1 !re=e1 mean1 n ! #a-quantum orbit1 b ! inn]mo/ possible "u ! exi/+ circum/ances4 ,! f9al result w be t ! electrons are di/ribut$ 9 gr\ps1 :i* are *>act]iz$ ea* by _! quantum numb]s 9 su* a way t pass+ f ! nucleus to ! surface ( ! atom1 ! successive gr\ps correspond to successive integ] values ( ! quantum numb]1 ! inn]mo/ gr\p be+ *>act]iz$ by ! quantum numb] "o4 ,moreov]1 ea* gr\p is subdivid$ into sub-gr\ps correspond+ to ! diff]5t values :i* ! auxili>y quantum numb] may take4 ,t ! electrons fir/ collect$ keep ! latecom]s at an appropriate di/ance mu/ be und]/ood ) res]vations2 a new electron mov+ 9 an elongat$ orbit c v well come into ! t]ritory already occupi$2 9 fact1 x may come clos] to ! nucleus ?an "s ( ! inn]mo/ gr\ps ( electrons4 ,9 case an out] electron ?us dives into ! inn] gr\ps1 x makes a v %ort visit1 travell+ ab\t ! nucleus l a comet :i* at "o "t on its elongat$ orbit comes 9 among ! planets & p]haps draws clos] to ! sun ?an ! inn]mo/ planet1 b dur+ ! great] "p ( its travell+ "t moves 9 di/ant regions beyond ! b\nd>ies ( ! planet>y sy/em4 ,x is a v important *>act]i/ic ( ! ,bohr !ory ( atomic ar*itecture t ! out] electrons ?us p5etrate f> into ! int]ior ( ! atom & ?us *a9 ! :ole sy/em toge!r4 ,su* a 8comet electron0 has1 h[ev]1 a motion ( a v diff]5t nature f t ( a comet 9 ! sol> sy/em4 ,let u suppose t ! nucle> *>ge is #ee 7,caesium71 t !re already are fifty-f\r electrons ga!r$ tightly ab\t ! nucleus1 & t ,no4 #ee 9 an orbit consi/+ ( oblong loops moves f> away f ! nucleus1 b at c]ta9 times comes 9 close to x4 ,!n1 = ! great] "p ( its orbit1 ?is electron w be subject to approximately ! same attraction z ! attraction t[>ds "o s+le *>ge1 z a hydrog5 nucleus2 b :5 ,no4 #ee comes )9 ! fifty-f\r electrons x w = a v %ort "t be influ5c$ by ! entire nucle> *>ge #ee4 ,toge!r ) ! ne>ness ( ! nucleus1 ?is w cause ,no4 #ee to acquire a rem>kably high velocity & to move 9 an orbit q diff]5t f ! elliptical "o x foll[$ outside4 ,moreov]1 ! great velocity ( ! electron dur+ its %ort visit to ! nucleus is 9 a consid]able degree det]m9ative ( its pr9cipal quantum numb]2 ?is w be high] ?an w\ld be expect$ f ! dim5sions ( ! out] "p ( ! orbit if we suppos$ ! motion to take place ab\t a hydrog5 nucleus 7cf4 ,figs4 #bg & #bi74 ,aft] ^! g5]al rem>ks we %all try 9 a few l9es to sket* ! ,bohr !ory ( ! /ructure ( ! atomic sy/ems f ! simple/ to ! mo/ complicat$4 ,we %all n exam9e ! entire p]iodic sy/em ) its n9ety-two elem5ts1 b "h & !re we %all br+ to light a trait :i* w illu/rate ! problem--p>tly 9 connection ) ! s*ematic repres5tations 9 ! atomic diagrams at ! end ( ! book4 ,description ( ! ,atomic ,diagrams4 ,! curves drawn repres5t p>ts ( ! orbital loops ( ! electrons 9 ! neutral atoms ( diff]5t elem5ts4 ,al?\gh ! attempt has be5 made to give a true picture ( ^! orbits z reg>ds _! dim5sions1 ! draw+s mu/ /ill be consid]$ z l>gely symbolic4 ,?us 9 reality ! orbits d n lie 9 ! same plane1 b are ori5t$ 9 diff]5t ways 9 space4 ,x w\ld h be5 impracticable to %[ ! diff]5t planes ( ! orbits 9 ! figure4 ,moreov]1 !re is /ill a good deal ( unc]ta9ty z to ! relative positions ( ^! planes4 ,on ?is acc\nt ! orbits belong+ to ! same sub-gr\p1 i4e41 designat$ by ! same quantum numb]s1 are plac$ 9 a symmetric s*eme 9 ! sket*4 ,= gr\ps ( circul> orbits ! rule has be5 foll[$ to draw only "o ( !m z a circle1 :ile ! o!rs 9 ! simpl] atoms are drawn 9 projection z ellipses )9 ! circle1 & 9 ! m complicat$ atoms are omitt$ entirely4 ,! two circul> orbits ( ! helium atom are bo? drawn 9 projection z ellipses4 ,fur!r1 = ! sake ( cle>ness1 no attempt has be5 made to draw ! inn] loops ( ! non-circul> orbits ( electrons :i* dive into ! int]ior ( ! atom4 ,9 li?ium only1 ! inn] loop ( ! orbit ( ! #b electron has be5 %[n by dott$ l9es4 ,9 ord] to di/+ui% ! gr\ps ( orbits ) diff]5t pr9cipal quantum numb]s two col\rs h be5 us$1 r$ & black1 ! r$ indicat+ ! orbits ) unev5 quantum numb]s1 z #a1 #c1 #e1 ! black ^? ) ev5 quantum numb]s1 z #b1 #d1 #f4 ,:]ev] possible ! nucleus is indicat$ by a black dot2 b 9 ! sket*es ( atoms ) high] atomic numb]s ! #a-quantum orbits are m]g$ into "o little cross & ! nucleus has be5 omitt$4 ,x %\ld be notic$ t ! radium atom is drawn on a scale twice z great z t = ! o!r atoms4 ,we %all beg9 ) ! capture ( ! fir/ electron4 ,if ! nucleus is a hydrog5 nucleus ! hydrog5 atom is complet$ :5 ! electron has come into ! #a orbit1 a circle ) diamet] ( ab\t #aj cm4 7cf4 ! diagram74 ,if ! nucleus _h _h a great] nucle> *>ge ! ,no4 #a electron w\ld h behav$ 9 ! same way1 b ! radius ( its orbit w\ld h be5 less 9 ! same ratio z ! nucle> *>ge 0 great]4 ,= a lead nucleus1 ) *>ge 7atomic numb]7 #hb1 ! radius ( ! #a orbit is _/ t ( ! hydrog5 #a orbit4 ,s9ce atoms ) high atomic numb]s ?us collect ! electrons m tightly ab\t !m x is und]/&able t1 9 spite ( _! great] numb] ( electrons1 !y c be ( ! same ord] ( magnitude z ! simpl] atoms4 ,let u n[ exam9e ! helium atom4 ,! fir/ electron1 :i* its nucleus 7*>ge #b7 cat*es1 moves z %[n 9 a circle #a1 b ) a small] radius ?an 9 ! case ( ! hydrog5 atom4 ,electron ,no4 #b c be caught 9 diff]5t ways1 & ! clos] /udy ( ! conditions prevail+ "h1 :i* are /ill comp>atively simple s9ce !re are only two electrons1 has be5 ( greate/ importance 9 ! fur!r developm5t ( ! :ole !ory4 ,we _c g into x "h1 b mu/ cont5t ourselves ) say+ t ! /able f9al result ( ! b9d+ ( ! second electron consi/s 9 ! two electrons mov+ 9 circul> #a-quantum orbits ( ! same size ) _! planes mak+ an angle ) ea* o!r 7cf4 ! diagram74 ,?is /ate has a v /able "*1 & ! helium atom is !re=e v dis9cl9$ to int]play ) o!r atoms1 ) o!r helium atoms z well z ) ^? ( o!r elem5ts4 ,helium is !re=e monatomic & a *emically inactive gas4 ,9 all atomic nuclei ) high] *>ges ?an ! helium nucleus ! fir/ two orbits are also b\nd into two #a-quantum circul> orbits at an angle ) ea* o!r2 ?is gr\p _c take up any new electron hav+ ! same pr9cipal quantum numb]4 ,x takes on an indep5d5t exi/5ce & =ms ! inn]mo/ electron gr\p 9 all atoms ( atomic numb] high] ?an #b4 ,electron ,no4 #c w accord+ly n be b\nd 9 ! same gr\p ) #a & #b4 ,x mu/ be satisfi$ ) a #b-quantum orbit1 #b1 :i* consi/s ( oblong loops1 &1 :5 ne>e/ ! nucleus1 comes into ! t]ritory ( ! #a-quantum orbits4 ,x is b loosely b\nd comp>$ to ! fir/ two electrons1 & ! li?ium atom1 :i* has only ?ree electrons1 c !re=e easily let ,no4 #c loose s t ! atom becomes a positive ion4 ,li?ium is !re=e a /rongly electropositive monoval5t metal4 ,! elem5t b]yllium 7,no4 #d7 w probably h two electrons 9 ! orbits #b2 x w !re=e be dival5t4 ,b dur+ ! %ort visit ( ^! electrons to ! nucleus !y are subject to a great] nucle> *>ge ?an 9 li?ium4 ,! #b electrons are !re=e1 9 b]yllium1 m firmly b\nd ?an 9 li?ium1 & ! electropositive "* ( b]yllium is !re=e less m>k$4 ,we h some?+ ess5tially new 9 ! boron atom 7atomic ,no4 #e7 :]e ! two electrons ,no4 #c & ,no4 #d are tak5 into #b orbits1 b :]e ,no4 #e w v probably be b\nd 9 a circul> #b orbit4 ,h[ ! conditions w be 9 ! normal /ate ( ! foll[+ atoms prec$+ neon is n kn[n ) c]ta9ty4 ,we only "k t ! electrons com+ aft] ! fir/ two w be captur$ 9 #b-quantum orbits1 ! dim5sions ( :i* get small]1 accord+ z ! atomic numb] increases4 ,! neon atom 7comp>e ! diagram7 has a p>ticul>ly /able /ructure1 bo? 8clos$0 & symmetric1 :i* besides two #a-orbits conta9s f\r electrons 9 #b orbits & f\r electrons 9 #b orbits4 ,z reg>ds ! f\r electrons 9 #b orbits1 !y d n h symmetrical positions at e mom5t or move simultane\sly ei!r t[>ds or away f ! nucleus2 on ! contr>y1 x mu/ be assum$ t ! electrons come close/ to ! nucleus at diff]5t mom5ts at equal int]vals ( "t4 ,! "n ( in]t or inactive gases is giv5 to ! entire s]ies ( helium 7#b71 neon 7#aj71 argon 7#ah71 krypton 7#cf71 x5on 7#ed7 & niton 7#hf71 ! ,o-column 9 ! p]iodic sy/em giv5 9 ! table on p4 #bc4 ,all ^! elem5ts are monatomic & q unwill+ to ent] into *emical comp\nds ) o!r elem5ts 7al?\gh !re is ab\t #a p] c5t4 ( argon 9 ! air ab\t u ?is elem5t has1 on ?is acc\nt1 escap$ ! obs]vation ( *emi/s until ab\t #ahie1 :5 x 0 discov]$ by ! ,engli% *emi/1 ,ramsay74 ,?is complete *emical inactivity is expla9$ by ! fact t ! atoms ( all ^! elem5ts h a nicely f9i%$ 8ar*itecture0 ) all ! electrons firmly b\nd 9 symmetrical configurations4 ,!y may be said to =m ! mile po/s ( ! p]iodic sy/em1 & to be ! ideals t[>ds :i* ! o!r atoms aspire4 ,! table %[s h[ ! electrons 9 ! atoms ( ^! gases are divid$ among ! types ( orbits correspond+ to ! diff]5t quantum numb]s4 ,,table ,,%[+ ,,! ,,di/ribution ,,( ,,! ,,electrons ,,( ,,diff]5t ,,orbital ,,types ,,9 ,,! ,,neutral ,,atoms ,,( ,,! ,,inactive ,,gases4 ---------------------------------------- ------------ ,quantum ,numb]s4 ,atomic------------------------------ ,numb] #a #b #b #c #c #c #d #d #d #d ---------------------------------------- --- ,helium #b #b ,neon #aj #b #d #d ,argon #ah #b #d #d #d #d - ,krypton #cf #b #d #d #f #f #f #d #d - - ,x5on #ed #b #d #d #f #f #f #f #f #f - ,niton #hf #b #d #d #f #f #f #h #h #h #h 8 #aah #b #d #d #f #f #f #h #h #h #h ---------------------------------------- --- ---------------------------------------- --------------------------- ,quantum ,numb]s4 ,atomic--------------------------------- -------- ,numb] #e #e #e #e #e #f #f #f #f #f #f #g #g #g ---------------------------------------- -------------- ,helium #b ,neon #aj ,argon #ah ,krypton #cf ,x5on #ed #d #d - - - ,niton #hf #f #f #f - - #d #d - - - - 8 #aah #h #h #h #h - #f #f #f - - - #d #d - ---------------------------------------- -------------- ,! elem5ts fluor9e1 oxyg5 & nitrog5 c atta9 ! ideal neon-ar*itecture by b9d+ respectively "o1 two & ?ree additional electrons4 ,naturally !y d n become neon atoms1 b m]ely negative atomic ions ) s+le1 d\ble or triple *>ge2 & _! t5d5cy 9 ?is direction appe>s 9 _! "* ( monoval5t1 dival5t & trival5t electronegative elem5ts respectively4 ,if we return to c>bon x c probably n become a tetraval5t negative ion by b9d+ f\r free electrons2 b 9 ! typical c>bon comp\nd1 me?ane 7,,*71 ! neon ideal is realiz$ 9 ano!r mann]4 ,9 fact1 x is reasonable to assume t ! f\r electrons ( ! hydrog5 atoms toge!r ) ! six ( ! c>bon atom give approximately a neon-ar*itecture4 ,! f\r hydrog5 nuclei naturally _c be comb9$ ) ! c>bon nucleus2 ! mutual repulsions keep !m at a di/ance4 ,!y w probably assume v symmetrical positions )9 ! electron sy/em :i* holds !m toge!r4 ,! nitrog5 atom may 9 a simil> way f9d completion 9 a neutral molecule ) neon-ar*itecture1 if x unites ) ?ree hydrog5 atoms to =m ammonia ,,nh2 b ! ?ree hydrog5 nuclei1 al?\gh hav+ symmetrical positions1 w n lie 9 ! same plane z ! nitrog5 nucleus4 ,! electric c5tre ( gravity = ! positive nuclei w !re=e n co9cide ) ! c5tre ( gravity = ! negative electron sy/em4 ,! molecule obta9s ?us :at might be call$ a positive & a negative pole1 & ?is dipol> "* appe>s 9 ! electrical action ( ammonia 7its dielectric con/ant74 ,some?+ simil> holds true = ! wat] molecule1 :]e1 9 a neon-ar*itecture ( electrons1 9 addition to ! oxyg5 nucleus 9 ! c5tre !re are two hydrog5 nuclei :i* are n co-l9e> ) ! oxyg5 nucleus4 ,if we g on f neon 9 ! p]iodic sy/em we come to sodium 7#aa74 ,:5 ! sodium nucleus captures electron ,no4 #aa1 ?is _c f9d room 9 ! neon-ar*itecture =m$ by ! fir/ t5 electrons4 ,s9ce ! elev5? electron ?us _c f9d a place 9 ei!r a #b or a #b orbit1 x is b\nd 9 a #c orbit 7cf4 ,fig4 #bi & diagram at ! end74 ,! atom !n has a "* l t ( ! li?ium atom1 & we c !re=e und]/& ! *emical relation%ip betwe5 ! two elem5ts1 :i* are bo? monoval5t electropositive metals4 ,we %all n dwell long] ^u ! individual elem5ts ( ! atomic s]ies4 ,if we pass f neon ?r\gh sodium 7#aa71 magnesium 7#ab71 alum9ium 7#ac71 etc41 to argon 7#ah71 we get :at is ess5tially a repetition ( ! situation 9 ! s]ies f li?ium to neon4 ,we fir/ get two orbits ( ! #c type 9 magnesium1 a #c orbit is = ! fir/ "t add$ 9 alum9ium1 & = ! atomic numb] #ah1 eight #c-quantum orbits1 toge!r ) ! eight orbits ( ! inn] #b-quantum gr\p & ! two ( ! inn]mo/ #a-quantum gr\p1 give ! symmetric ar*itecture ( argon 7cf4 table on p4 #aif1 & diagram at ! end74 ,! ar*itecture ( ! argon atom is 9 a c]ta9 s5se less complete ?an t ( ! neon atom4 ,9 argon !re are inde$ f\r orbits ( ! #c type & f\r ( ! #c type1 b ! ?ird k9d ( #c-quantum orbit1 ! circul> #c "o1 is miss+4 ,nor does x appe> 9 ! next elem5t1 potassium 7#ai74 ,! electron ,no4 #ai pref]s1 in/ead ( ! #c orbit1 ! #d orbit1 :i* consi/s ( oblong loops & :i* gives a firm] b9d+ because x dives 9 among ! electrons b\nd e>li]1 :ile ! circle #c w\ld lie outside !m all4 ,we ?us obta9 an atom ( type simil> to ! li?ium & sodium atoms4 ,b ! slight$ #c pa? lies1 s to speak1 on ! wat* to /eal a place = itself 9 ! neutral atom1 & ?is has grave results = ! subsequ5t developm5t4 ,ev5 9 calcium 7#bj71 aft] ! fir/ eighte5 electrons are b\nd 9 ! argon ar*itecture1 bo? ! n9ete5? & ! tw5tie? g into a #d orbit1 & ! behavi\r ( calcium is l t ( magnesium4 ,b s9ce ! increas+ nucle> *>ge means = ! electron ,no4 #ai a decrease 9 ! dim5sions & an increase 9 ! b9d+ ( ! orbits correspond+ to ! quantum numb] #c1 a po9t w f9ally be atta9$ :]e ! #c orbit ( ! n9ete5? electron lies )9 ! b\nd>ies ( :at may be call$ ! argon sy/em1 i4e41 ! ar*itecture correspond+ to ! fir/ eighte5 electrons1 & corresponds to a /rong] b9d+ ?an a #d orbit w\ld d4 ,9 sc&ium 7#ba7 ! #c-type orbit occurs = ! fir/ "t 9 ! neutral atom & w n only come into competition ) ! #d type1 b w also cause a di/urbance 9 ! #c-quantum gr\ps1 :i* 9 ! foll[+ elem5ts mu/ und]go recon/ruction4 ,z long z ?is la/s ! situation is v complicat$ & unc]ta94 ,:5 ! reorganization is almo/ complet$1 we come to ! blott+ out ( *emical diff]5ces1 p>ticul>ly kn[n f ! triad1 iron1 cobalt & nickel4 ,moreov]1 !re comes a fluctuation 9 ! val5cy ( ! elem5ts4 ,iron c1 z has be5 said1 be dival5t1 trival5t or hexaval5t4 ,?is oscillation 9 val5cy beg9s 9 titanium4 ,we %\ld p]haps expect t ! recon/ruction w\ld be complet$ long be=e nickel 7#bh7 is rea*$1 because ev5 ) tw5ty-two electrons we c\ld get f\r orbits ( ea* ( ! #c-quantum types 7#c1 #c & #c72 b f ! *emical facts we are l$ to assume t 9 a complet$ gr\p ( #c-quantum orbits !re c be room = six electrons 9 ea* sub-gr\p4 ,at fir/ sight we %\ld1 !n1 expect ! end ( ! recon/ruction ) nickel1 :i* has inde$ eighte5 electrons m ?an neon :]e ! gr\p ( #b-quantum orbits 0 complet$4 ,we might expect t nickel w\ld be an in]t elem5t 9 ! s]ies ) helium1 neon1 & argon4 ,on ! contr>y1 nickel m]ely imitates cobalt4 ,?is is expla9$ by ! fact t ! gr\p ( eighte5 #c-quantum orbits1 al?\gh x has a symmetric ar*itecture1 is weakly con/ruct$ if ! nucle> *>ge is n suffici5tly l>ge4 ,! b9d+ ( ?is gr\p is too weak = x to exi/ z ! out] gr\p 9 a neutral atom4 ,9 nickel ! electrons1 9 a less symmetrical mann]1 w probably arrange !mselves ) sev5te5 #c-quantum orbits & "o #d-quantum orbit4 ,! gr\p ( eighte5 #c-quantum orbits becomes /able1 h[ev]1 :5 ! nucle> *>ge is equal to or l>g] ?an #bi1 9 :i* case x c become ! out] gr\p 9 a positive ion4 ,9 ?is we f9d ! explanation ( ! prop]ties ( ! atom ( copp]4 ,! neutral copp] atom has its tw5ty-n9? electron b\nd 9 a #d orbit consi/+ ( oblong loops 7cf4 diagram at ! end72 ?is electron c easily be fre$ & leaves a positive monoval5t copp] ion ) a symmetrical ar*itecture4 ,ev5 "u ^! circum/ances1 al?\gh possess+ a c]ta9 /ability1 ! ion is n v firmly con/ruct$4 ,?us ! fact t copp] c be bo? monoval5t & dival5t1 mu/ be expla9$ by ! assumption t = a nucle> *>ge #bi1 ! #c-quantum gr\p /ill easily loses an electron4 ,:5 we come to z9c 7#cj7 ! gr\p ( eighte5 is m firmly b\nd2 z9c is a pron\nc$ dival5t metal :i* 9 its prop]ties rem9ds u ( calcium & magnesium4 ,f z9c 7#cj7 to krypton 7#cf7 we h a s]ies ( elem5ts :i* 9 a c]ta9 way repeat ! s]ies f magnesium 7#ab7 to argon 7#ah74 ,9 ,fig4 #cd is %[n ,bohr's arrangem5t ( ! p]iodic sy/em 9 :i* ! sy/ematic correlation ( ! prop]ties ( ! elem5t appe>s some:at cle>] ?an 9 ! usual plan 7cf4 p4 #bc74 ,x %[s great simil>ity ) an arrangem5t propos$ ne>ly ?irty ye>s ago by ! ,dani% *emi/1 ,julius ,?oms54 ,! elem5ts f sc&ium to nickel1 :]e1 9 ! neutral atom1 ! electron gr\p ( #c-quantum orbits is 9 a /ate ( recon/ruction1 are plac$ 9 a frame2 ! neutral oblique l9es connect elem5ts :i* are 8homolog\s10 i4e41 simil> 9 *emical & physical 7spectral7 respect4 ,illu/ration3 ,,fig4 #cd4--,! p]iodic sy/em ( ! elem5ts4 ,! elem5ts :]e an inn] gr\p ( orbits is 9 a /age ( recon/ruction are fram$4 ,! oblique l9es connect elem5ts :i* 9 physical & *emical respects h simil> prop]ties4 ,9 krypton 7#cf7 we aga9 h a /able ar*itecture ) an out] gr\p ( eight electrons1 f\r 9 #d orbits & f\r 9 #d orbits4 ,ow+ to ! appe>ance ( #d orbits 9 ! normal /ate ( ! atoms ( elem5ts ) atomic numb] high] ?an #ch1 !re foll[s 9 ! fif? p]iod ( ! natural sy/em a recon/ruction & provisional completion ( ! #d-quantum orbits to a gr\p ( eighte5 electrons1 :i* %[s a great simplicity ) ! completion ( ! #c-quantum gr\p 9 ! f\r? p]iod4 ,9 ,fig4 #cd ! elem5ts :]e ! #d-quantum gr\p is 9 a /ate ( recon/ruction are fram$4 ,! #d-quantum gr\p ) eighte5 electrons is ( m /able con/ruction ?an ! gr\p ( eighte5 #c-quantum orbits 9 ! elem5ts ) an atomic numb] l[] by eighte54 ,?is is due to ! fact t all ! orbits 9 ! fir/-m5tion$ gr\p are oblong & !re=e moor$1 s to say1 9 ! inn] gr\ps1 :ile 9 ! complete gr\p ( #c-quantum orbits !re are six circul> orbits4 ,?is is ! reason :y silv]1 9 contra/ to copp]1 is monoval5t4 ,! next inactive gas is x5on 7#ed71 :i* outside ( ! #d-quantum gr\p has a gr\p ( eight electrons 9 #e-quantum orbits1 f\r 9 #e orbits & f\r 9 #e orbits4 ,we notice t 9 x5on ! gr\p ( #d-quantum orbits /ill lacks ! #d orbits4 ,on ! !ory we mu/1 !re=e1 expect to meet a new process ( completion & recon/ruction :5 proce$+ 9 ! sy/em ( ! elem5ts4 ,! !oretical argum5t is simil> to t :i* applies 9 ! case ( ! completion ( ! #c-quantum gr\p :i* takes place 9 ! f\r? p]iod ( ! natural sy/em4 ,9 fact1 9 ! =mation ( ! normal atoms ( ! elem5ts next aft] x5on1 caesium1 #ee1 & b>ium1 #ef1 ! fifty-f\r electrons fir/ captur$ w =m a x5on configuration1 :ile ! fifty-fif? electron w be b\nd 9 a #f orbit1 consi/+ ( v oblong loops1 :i* repres5ts a mu* /rong] b9d+ ?an a circul> #d orbit4 ,calculation %[s1 h[ev]1 t ) increas+ nucle> *>ge !re mu/ soon appe> an elem5t = :i* a #d orbit w repres5t a /rong] b9d+ ?an any o!r orbit4 ,?is is actually ! case 9 c]ium 7#eh71 & />t+ f ?is elem5t we meet a s]ies ( elem5ts :]e1 9 ! normal neutral atom1 ! #d-quantum gr\p is 9 a /ate ( recon/ruction4 ,?is recon/ruction mu/ occur f> )9 ! atom1 s9ce ! gr\p ( eighte5 #d-quantum orbits 9 x5on is already cov]$ by an out] gr\p ( eight #e-quantum orbits4 ,! result is a :ole s]ies ( elem5ts ) v slight outw>d diff]5ces betwe5 _! neutral atoms1 & !re=e ) v simil> prop]ties4 ,?is is ! r>e e>?s gr\p1 :i* 9 su* a /range way seem$ to break d[n ! ord] ( ! natural sy/em 7cf4 p4 #ba71 b :i* ?us f9ds its natural explanation 9 ! quantum !ory ( ! /ructure ( ! atom4 ,! elem5ts 9 :i* ! #d-quantum gr\p is 9 a /ate ( recon/ruction are1 9 ,fig4 #cd1 enclos$ 9 ! inn] frame 9 ! six? p]iod4 ,moreov]1 9 ! out] frame all elem5ts are enclos$ :]e ! gr\p ( #e-quantum orbits is 9 a /ate ( recon/ruction1 :i* />t$1 ev5 be=e c]ium 9 lan?anum 7#eg71 :]e ! fifty-fif? electron 9 ! normal /ate is b\nd 9 a #e orbit4 ,! elem5t cassiopeium1 ) atomic numb] #ga1 :i* is ! la/ ( ! r>e e>?s1 /&s j outside ! inn] frame1 because 9 ! normal neutral atom ( ?is elem5t ! #d-quantum gr\p is j complet$2 ?is gr\p1 in/ead ( eighte5 electrons ) six electrons 9 ea* sub-gr\p1 consi/s n[ ( ?irty-two electrons ) eight electrons 9 ea* sub-gr\p4 ,! !ory 0 able to pr$ict t ! elem5t ) atomic numb] #gb1 :i* until a %ort "t ago _h nev] be5 f\nd1 & ! prop]ties ( :i* _h be5 ! subject ( "s discussion1 mu/ 9 its *emical prop]ties diff] consid]ably f ! trival5t r>e e>?s & %[ a resemblance to ! tetraval5t elem5ts zirconium 7#dj71 & ?orium 7#ij74 ,?is expectation has rec5tly be5 confirm$ by ! "w ( ,hevesy & ,co/] 9 ,cop5hag51 :o h obs]v$1 by means ( ,x-ray inve/igations1 t mo/ zircon m9]als conta9 consid]able quantities 7#a to #aj p] c5t47 ( an elem5t ( atomic numb] #gb1 :i* has *emical prop]ties resembl+ v mu* ^? ( zirconium1 & :i* on ?is acc\nt _h hi!rto n be5 detect$ by *emical inve/igation4 ,a prelim9>y inve/igation ( ! atomic weight ( ?is new elem5t1 = :i* its discov]]s h propos$ ! "n hafnium 7,hafnia ,cop5hag571 gave values ly+ betwe5 #agh-ahj1 9 accordance ) :at might be expect$ f ! atomic weight ( ! elem5ts 7#ga7 & 7#gc74 7,cf4 p4 #bc47 ,! fur!r completion ( ! gr\ps ( #e- & #f-quantum orbits1 :i* 9 ! r>e e>?s _h tempor>ily come to a /&/ill1 is resum$ 9 hafnium & goes on 9 a way v simil> to t 9 :i* ! #d- & #e-quantum gr\ps 9 ! fif?1 & ! #c- & #d-quantum gr\ps 9 ! f\r? p]iod und]w5t completion4 ,?us ! recon/ruction ( ! #e-quantum gr\p :i* began 9 lan?anum1 & :i* receives a *>act]i/ic expression 9 ! triad ( ! plat9um metals1 has come to a provisional conclusion 9 gold 7#gi71 gold be+ ! fir/ elem5t outside ! two frames :i*1 9 ,fig4 #cd1 appe> 9 ! six? p]iod4 ,! neutral gold atom possesses1 9 its normal /ate--besides two #a-quantum orbits1 eight #b-quantum orbits1 eighte5 #c-quantum orbits1 ?irty-two #d-quantum orbits & eighte5 #e-quantum orbits--"o loosely b\nd electron 9 a #f orbit4 ,9 niton 7#hf71 f9ally1 we meet aga9 an inactive gas1 ! /ructure ( ! atom ( :i* is indicat$ 9 ! table on p4 #aif4 ,9 ?is elem5t ! diff]5ce betwe5 nucle> & electron prop]ties appe>s v conspicu\sly1 s9ce ! /ructure ( ! electron sy/em is p>ticul>ly /able1 :ile t ( ! nucleus is un/able4 ,niton1 9 fact1 is a radioactive elem5t :i* is kn[n 9 ?ree isotopic =ms2 "o ( ^! is ! dis9tegration product ( radium1 ! s-call$ radium emanation2 x !n has a v brief life4 ,9 ! c\rse ( f\r days ov] half ( ! nuclei 9 a giv5 quantity ( radium emanation w explode4 ,9 ! diagram at ! end ( ! book1 z an example ( an atom ) v complicat$ /ructure1 !re is giv5 a s*ematic repres5tation ( ! atom ( ! fam\s elem5t radium1 on a scale twice z l>ge z ! "o us$ 9 ! o!r atoms4 ,x foll[s cle>ly en\gh1 f :at has be5 said 9 ,*ap4 ,,iv41 t ! /ructure ( ! electron sy/em has no?+ to d ) ! radioactivity4 ,all ! rem>kable radiation activities are due to ! nucleus itself4 ,!re has n ev5 be5 room 9 ! figure to draw ! nucleus2 ! #a-quantum orbits consi/ only ( a small cross1 & 9 ! o!r gr\ps we h cont5t$ ourselves ) summ>y indications4 ,! electron sy/em1 ) its eighty-eight electrons1 is1 h[ev]1 9 itself v int]e/+1 ) its symmetry 9 ! numb] ( electrons 9 ! diff]5t gr\ps4 ,9 ! diff]5t quantum gr\ps f #a to #g !re are f\nd respectively two1 eight1 eighte51 ?irty-two1 eighte51 eight & two electrons4 ,! la/ gr\p is naturally ( a v diff]5t nature f ! fir/2 !y are 8val5ce electrons10 :i* easily get loose & leave beh9d a positive radium ion ) /able niton ar*itecture4 ,radium !n belongs to ! family ( ! dival5t metals1 magnesium1 calcium1 /rontium & b>ium4 ,f\r places f radium is uranium 7#ib7 & ! end ( ! j\rney1 if we re/rict ourselves to ! elem5ts :i* are kn[n to exi/4 ,"o c\ld v well cont9ue ! build+-up process /ill fur!r & discuss :at /ructure w\ld h to be assum$ = ! atoms ( ! elem5ts ) high] atomic numb]s4 ,t !y _c exi/ is n ! fault ( ! electron sy/em b ( ! nuclei1 :i* w\ld become too complicat$ & too l>ge to be /able4 ,9 ! table on p4 #aif !re is %[n ! probable /ructure ( ! atom ( ! in]t gas foll[+ niton2 x mu/ be assum$ to h "o hundr$ & eighte5 electrons di/ribut$ 9 gr\ps ( two1 eight1 eighte51 ?irty-two1 ?irty-two1 eighte5 & eight among ! quantum gr\ps f #a to #g4 ,z has be5 said1 9 all ?is symmetrical /ructure ( ! atoms ( ! elem5ts1 ,bohr has 9 _m cases _h to rely ^u g5]al consid]ations ( ! in=mation t obs]vation gives ab\t ! prop]ties ( ! individual elem5ts4 ,x mu/1 h[ev]1 n be =gott5 t ! backbone ( ! !ory is & rema9s ! g5]al laws ( ! quantum !ory1 appli$ to ! nucleus atom 9 ! same way z !y orig9ally 7 appli$ to ! hydrog5 atom1 lead+ !reby to ! int]pretation ( ! hydrog5 spectrum4 ,we h1 fur!r1 a mo/ /rik+ evid5ce z to ! correctness ( ,bohr's ideas 9 ! fact t n only d ! pictures ( ! atoms :i* he has drawn agree ) ! kn[n *emical facts ab\t ! elem5ts1 b !y are also able to expla9 9 ! mo/ satisfactory mann] possible ! mo/ ess5tial features ( ! *>act]i/ic ,x-ray spectra ( ! diff]5t elem5ts1 a field we %all n ent] ^u "h4 ,9 all t has be5 said above we h be5 consid]+ ! ,bohr !ory simply z a means ( ga9+ a deep] und]/&+ ( ! laws :i* det]m9e activities 9 ! atomic _w4 ,p]haps we %all n[ be ask$ if we c 8utilize0 ! !ory1 or1 9 o!r words1 if x c be put to practical use4 ,to ?is natural & n unw>rant$ "q we may fir/ give ! v g5]al answ]1 t progress 9 our k ( ! laws ( nature always contributes soon] or lat]1 directly or indirectly1 to increase our ma/]y ov] nature4 ,b ! connection betwe5 sci5ce & practical application may be m or less conspicu\s1 ! pa? f sci5ce to practical application m or less smoo?4 ,x mu/ be admitt$ t ! ,bohr !ory1 9 its pres5t /ate ( developm5t1 h>dly leads to results ( direct practical application4 ,b s9ce x %[s ! way to a m ?or\gh und]/&+ ( ! details 9 a great numb] ( physical & *emical processes1 :]e ! peculi> prop]ties ( ! diff]5t elem5ts play p>ts ( decid$ importance1 !n 9 reality x (f]s a weal? ( possibilities = mak+ pr$ictions ab\t ! c\rse ( ! processes--pr$ictions :i* und\bt$ly 9 ! c\rse ( "t w be ( practical use 9 _m ways4 ,9 ?is connection ! discov]y ( ! elem5t hafnium1 discuss$ on p4 #bjd1 may be m5tion$4 ,x mu/ be = ! future to %[ :at ! ,bohr !ory c d = te*nical practice4 ,bel[ is giv5 an explanation ( ! diff]5t symbols :i* occur at v>i\s places 9 ! book2 also ! values ( important physical con/ants4 #a m4 #a metre2 #a cm4 #a c5timetre #jcid in*es4 #a #a micron #a_/ajjj ( a millimetre #jjjja cm4 #aj cm4 #a #a_/a1jjj1jjj ( a millimetre #aj cm4 #a cm4 #a cubic c5timetre4 #a g4 #a gram2 #a kg4 #a kilogram #bb p\nds4 #a kgm4 #a kilogrammetre 7! "w or ! en]gy requir$ to lift #a kg4 #a m474 #a erg #ajb #aj kgm4 #gdh #aj foot-p\nds4 repres5ts wave-l5g?4 repres5ts frequ5cy 7numb] ( oscillations 9 #a second74 repres5ts frequ5cy ( rotation 7numb] ( rotations 9 #a second74 n repres5ts an integ] 7p>ticul>ly ! ,bohr quantum numb]s74 ,! velocity ( light is c #c #aj cm4 p] second #ii #aj feet p] second4 ,! wave-l5g? ( yell[ sodium light is #jehi #ehi #bcb #aj in*es4 ,! frequ5cy ( yell[ sodium light is #ebf #aj vibrations p] second4 ,! numb] ( molecules p] cm4 at #j ,c4 & atmosph]ic pressure is ab\t #bg #aj4 ,! numb] ( hydrog5 atoms 9 #a g4 is ab\t #faj4 ,! mass ( a hydrog5 atom is #afe #aj g4 ,! elem5t>y quantum ( electricity is #dgg #aj 8electro/atic units40 ,! negative electric *>ge ( an electron is #a elem5t>y quantum 7#a negative *>ge74 ,! positive electric *>ge ( a hydrog5 nucleus is #a elem5t>y quantum 7#a positive *>ge74 ,! mass ( an electron is t ( ! hydrog5 atom4 ,! diamet] ( an electron is e/imat$ to be ab\t #c #aj cm4 ,! diamet] ( ! atomic nucleus is ( ! ord] ( magnitude #aj to #aj cm4 ,! diamet] ( a hydrog5 atom 9 ! normal /ate 7! diamet] ( ! fir/ /ation>y orbit 9 ,bohr's model7 is #ajef #aj cm4 ,! ,balm] con/ant ,k #cbi #aj4 ,! ,planck con/ant h #fed #aj4 ,an en]gy quantum is ,e h4 ,! ,balm]-,ritz =mula = ! frequ5cies ( ! l9es 9 ! hydrog5 spectrum is 7 #a #a 7 ,k 7 ------ - -------7 7 n n 7 ,illu/ration3 ,,diagrams ,,( ,,spectra ,,aft] ,,buns5 ,,& ,,kir*h(f ,illu/ration3 ,,/ructure ,,( ,,! ,,radium ,,atom ,illu/ration3 ,,ma9 ,,l9es ,,( ,,! ,,atomic ,,/ructure ,,( ,,"s ,,elem5ts