lewis (valence and the structure of atoms and molecules) (acs)

8/17/2019 Lewis (Valence and the Structure of Atoms and Molecules) (ACS)

1/169

dMolecules

YINTHEUNIVERSITY

ety

OMPANY,Inc.

WYORK,U.S.A.

P u b l

i c D o m a i n , G o o g l e - d i g i t i z e d

/ h t t p : / / w w w . h

a t h i t r u s t . o r g / a c c e s s_ u s e # p d - g o o g l e


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P u b l i c D o m a i n , G o o g l e - d i g i t i z e d

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etySeriesof

cMonographs

nteralliedConferenceofPureand

metinLondonandBrusselsinJuly,

calSocietywastoundertakethepro-

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cts.Atthesametimeit wasagreed

hCouncil,incooperationwiththe

etyandtheAmericanPhysicalSociety,

uctionandpublicationofCritical

ysicalConstants.TheAmerican

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o fieldsofchemicaldevelopment.

ocietynamedasTrustees,tomake

ntsforthepublicationofthemono-

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.;JohnE.Teeple,Treasurerofthe

ety,NewYorkCity;andProfessor

moreCollege.TheTrusteeshave

onoftheAmericanChemicalSociety

b) TechnologicMonographsbythe

nyofNewYorkCity.

htheCommitteeonNationalPolicy

Society,appointedtheeditors,named

ction,tohavechargeofsecuring

gcriticallythemanuscriptsprepared.

will endeavortoselecttopicswhich

authors whoarerecognizedasauthor-

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ON

ledgeinallbranchesofscience,and

asbeensorapidduring thelastfifty

edbythis developmenthavebeenso

ranyindividualtokeepin touchwith

fscienceoutsidehis ownspecialty.

theexaminationoftheliterature

ctsandsuchcompendiaasBeilstein's

enChemie,Richter'sLexikon,Ostwald's

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henChemieandtheEnglishand

emistry,itoftentakesagreatdeal

nowledgeavailableuponasingle topic.

whohavespentyearsinthestudy of

ingtocoordinatetheirknowledge

readableform,theyperformaservice

eirfellowchemists.

tionoftheusefulnessofreviewsof

mitteeoftheAmericanChemical

publicationofthe twoseriesofmono-

ofthe Society.

esaretobe servedbythesemono-

whosefulfilmentwillprobablyrender

most importantservice,istopresent

ponthechosentopicin.areadable

hoseactivitiesmaybealonga wholly

istsfailtorealizehowcloselytheir

nectedwithotherworkwhichonthe

romtheirown.Thesemonographs

m closercontactwiththeworkof

search.Thesecondpurposeis to

anchofsciencecoveredbythemono-

digestedsurveyof theprogress

nd bypointingoutdirectionsin

stobeextended.Tofacilitatethe

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e,whichwillenableanyoneinterested

moredetail.Iftheliteratureis so

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deofthosepapers whicharemost


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5

ooksmarksadistinctdeparturein

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an Americanchemicalliteraturewith-

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opicsofgeneralinterest;itis earnestly

erymemberofthevariousorganizations

ndustrieswill recognizetheimpor-

takesufficientinterestto justifyit.

IETY

ogicSeries:—

,HARRISONE.HOWE,Editor,

ERICK,

A.LIDBURY,.

URD.LITTLE,

WNSEND,


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ety

eriesofwhichthis bookisapart

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ercury.

7pages.Price$4.50.

ughS.Taylor.Price$3.50.

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Smith.273pages.Price$4.00.

phaParticlesandElectrons.

ges.Price$3.00.

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50.

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yJohnB.Tuttle.Price$2.50.

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gments.

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Manufacture.

00.

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the Silicates.ByRobertB.Sosman.

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unds.ByGeorgeW.Raiziss.Jo-

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entsoftheUniversityof

helpthisbookwouldnot

anyyearsof discussion

ndmolecularstructure,

sentedhave sprungfrom

an individual;sothatin

seditorforthis group.


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8/169

ofthissortbelongsto theephemeral

tudiedcarewhichiswarrantedin the

wlymovingbranchesofsciencewouldbeout

hepen ofajournalistwemustattempt

aseofcurrentthought,whichmayat any

oscopicabruptness.

thatsomeofthethingssaid inthisbook

d,but Itrustthatthese maybemattersof

ce.Duringthe sevenyearsthathaveelapsed

tionconcerningthestructureofthemolecule

micalbond,Ihavefoundlittleneedof sub-

eresetforth,althoughthere isnowmuchto

rkIshallhopethat therearenoserioussins

aresinsof omissionIamalreadyonlytoo

keeppacewiththe rapiddevelopmentsinso

ence,allofwhichcontributetoourknowl-

molecule,is,especiallyforonewhoisatbest

sibletask.

atom andthesamemoleculethatisbeing

mist,theinorganicchemistandthephysicist;

nclusionsofthespectroscopist,thefarmore

andimportantgeneralizationsofthestudent

mustcontribute,eachinduemeasure,to

rocosmoswhichappearstousthemore

comesmorenearlyrevealedtous. Itwas

hatIhavedevotedseveralofthe earlier

ring tothebetteracquaintanceofchemists

complishmentsofmodernphysics.


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9/169

HEORY17

ATTER,17.TheWorkofDalton,

,18.Prout'sHypothesisand

EORIESOFCHEMICALAFFINITY,

rDualisticHypothesis,20.Its

ofStructuralOrganicChemistry,

DiscontinuousNatureofElec-

rrhenius,21.Is thereanEssen-

olar"and"Nonpolar"Com-

CLAWANDTHECHEMIST'SPICTURE

eriodicTable,23.Rydberg'sOr-

fAtomicNumbersandtheWork

entFormofPeriodicTable,28.

29.Abegg'sNormalandContra-

ModeloftheAtom,31.Ruther-

2.Parson'sMagnetonTheory,

Lewis,33.

ERIESANDTHEPHYSICIST'SVIEWOF

eEmissionandAbsorptionof

mula,36.ThePickeringSeries,

RG,37.TheRydbergConstant,

iple,37.ASpectralLineasa

ncies,38.THEQUANTUMTHEORY,

uipartitionLaw,40.Planck's

einEquation,42.APARTIAL

HEORY,43.EnergyLevels,43.

-RAYSPECTRA,45.IONIZATION

IALS,46.BOHR'SATOMICMODEL,

alculationoftheRydbergCon-

riesasa HeliumSpectrum,49.

nstoBohr'sHypothesis,50.The

nOrbitasa UnitaryEntity,51.

2.MagneticMoment,53.Para-


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10/169

TIONOFTHETwoVIEWS;THEAR-

NSINTHEATOM55

haracterofAtomicStructure,55.

uilding-StoneofAtomicStruc-

ingInformation,56.TheIm-

ght,57. TheStillGreaterIm-

wo,or theElectronPair,57.

eMaximumNumberofElectrons

Groups,58.THEINNERSTRUC-

TOMS,58.CertainOrbitalArrange-

ObservedMagneticPhenomena,59.

ofElementaryMagnetsMayBe

softheShortPeriods,59. THE

TautomerismwithintheKernel,61.

cKernelsinVariousElementary

smofElementswithUncom-

MAININGPERIODS,65.Two

lUnexplainedbyQuantum

FATOMS;THEMODERNDUALISTIC

eTheory,68.TheWorkof

uitiesintheTerm"Valence,"68.

oryandItsInadequacy,71.The

hatTwoAtomsMayHoldElec-

EORYOFVALENCE;THECHEMICAL

tetsbytheSharingofElectrons,

TRONS,79.TheRarityofOdd

arProperties,80.ThePhysical

menonofPairing,81.THEBOND,

AlwaysaPair ofElectrons

tomicCentersandisHeldJointly

oms,81.TheTetrahedralChar-

82.TheEssentialIdentityof

polarCompounds,83.Electrical

tingof ElectronPairs,84.The

odernDualisticTheoryasan

FEATURESOFTHENEWVALENCE

edOxygen,86.TheUniversality

Types,86.TheQuadrivalence


/ h t t p : / / w w w . h



11/169

DTRIPLEBONDS88

eroftheDoubleBond,88.The

DoubleBond,89.TheBaeyer

atedDoubleBonds,90.The

,91.Huggins'TheoryofCon-

eofBenzene,92.THETRIPLE

velyGreaterSaturationofthe

xtentis theTripleBonda

FMULTIPLEBONDS,94.Mul-

mentsofthe FirstPeriodof

ry,95.RESUME,96.

NSTOTHERULEOFEIGHT...97

ShellContainsFewerthanFour

onCompounds,98.Sulfur

ounds,99.ATOMSWITHMORE

IRS,101.

DCOORDINATIONNUMBER... 104

104.TheNormalValenceof

ounds,105.ACommonType

ALENTHYDROGEN,109.The

WorkofLatimerandRodebush,

EOFNITROGEN,111.TheAmine

nds,111.DoCompoundsof

xist?113.TheWaldenInversion,

HANFOUR,113.Are"Valence"

er"Synonymous?,115.VALENCE

,116.TheStructureofSolids

,118.

OFELEMENTSWITHSMALLKERNELS119

ROGENANDHELIUM,121.

,122.BORON,123.TheUnique

ons,123.NITROGENANDCAR-

ssionofMultipleBonds,124.

uctureofNitrogen,Carbon

dDoubleAcetylideIon,127.

eandtheNitroso-Compounds,

RINE,129.ANewFormulafor

poundsbetweenFluorineand


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12/169

NPOSITIVEANDNEGATIVESTATES.131

rminology,131.THEPROBLEM

OMPOUNDSBETWEENNEGATIVE

dinaStateof Strain,133.The

ne,"133.TheLocalizationof

Molecule,133.TheBasicProp-

egativeState,134.APossible

positionofAlkoxylamine,135.

OFTHEELECTROCHEMICALTHEORY137

cChargeuponFurtherlonization,

CIDSANDBASES,138.TheIn-

tituentupontheStrengthof an

municatedthroughaChain,139.

eDibasicAcids,139.Certain

eStructureofInorganicAcids,

CIDSANDBASES,141.The

ein aGivenSolvent,142.A

EssentiallyAcidandBasicSub-

TORSDETERMININGDISSOCIATION,

nthe ElectronStructure,143.

on;Cis-andTrans-Acids,144.

WNANDGIBSON,144.Argu-

edAlternationinElectricalPolar-

idualAffinity,145.Possible

gaReaction,146.RESUME,146.

CEOFCHEMICALAFFINITY;AMAG-

47

esIncompetenttoAccountforthe

henomena,147.TheConjuga-

ets,147.TheEliminationof

heOddMoleculeRepresentsthe

alandMagneticUnsaturation,

MagneticFieldsbytheCoupling

herEliminationoftheResidual

mationofOctets,149.Distor-

StructureIncreasestheMobility

blestStructureOnein which

utedthrougha Molecule?150.

nsaturationDuetoDoubleBonds,

aramagnetism,152.IstheMag-

ltipleofaQuantumUnit?152.


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13/169

icalConjugationIsMagnetic

e,154.TheCarboxylGroup,

Diazo-Compounds,156.

NTINUITYOFPHYSICO-CHEMICAL

yofReactions,157.ItsInadequacy

s,157.THEDISCONTINUITY

,158.Resonanceandlonizationas

actions,158.Discontinuityinthe

8.TheMeaningof"Tight"and

theQuantumTheory,159.The

60.Catalysis,160.COLOR,160.

erColorTheoryinto theLan-

y,161.ColorasEvidenceofthe

s,161.TheMobilityofElec-

TUREOFQUANTUMTHEORY,

ofForce,164.TheNatureof

ometry,165.

6


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14/169

CTUREOF

r.

ateamonghistoriansofchemistryasto

alton'stwogreat generalizations.Which

oryorthelaw ofmultipleproportions?The

ton'smindthetwoideaswereessentially

ularstructureofmatter hadbeenafavorite

enturies,andatthebeginningofthe nineteenth

mongscientistsandlaymen."PoundSt.

ndconsideranyatom.. ."Boswellquoted

eearlier.

whoheldthisphilosophicaldoctrine

onesimple substanceasequivalenttoone

ks.Theideathata simplesubstanceiscom-

similarone toanother,mustthereforebe

art oftheintellectualheritageofthatperiod.

asthepossibilityof acrucialscientific

elementsandcompoundsaremadeupof

cparticles,eachparticleofacompoundsub-

egralnumberofparticlesof itscomponent

und,inthetwo hydrocarbonswhichwe

e,agivenamountofhydrogencombinedwith

eformeras inthelatter.In thetwooxides

o ofoxygentocarbontobe twiceasgreat

enhealsodiscoveredasimilar integral

desofnitrogen,hefelt justifiedinannounc-

tipleproportions.Thecrudityoftheexperi-

dthislaw,and thefactthathisanalysisof

enwasentirelyerroneous,indicateastrong

conclusionwhichhereached.

ionsconvertedaphilosophicspeculation

ence.Thetheoryof atomsandmolecules


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15/169

UCTUREOFATOMSANDMOLECULES

ofstoichiometry,butlateragain provedits

pmentofthe mechanicaltheoryofheat.

uryashortperiod ofscepticismastothe

uleswasabruptlyterminatedthroughthe

discovery.Itbecamepossibletocountthe

peinthehandsofPerrin(1908)permitted

smovingaboutinexactaccordwiththe

heory.Intheprocessesofradioactivityheavy

ntegratinginto lighteratoms,anditwas

Soddy(1903)thateachatomof helium

ubstanceproducesascintillationuponascreen

,sothatinasense weseetheindividual

counted,analyzed,decomposed.Even

stnucleusarebeing broughttolight.But

dtoproduceover-confidence.Foratimeit

andthebehaviorof theatomcouldbeinter-

hangeinthemodesofthought whichhad

alingwiththe massivebodiesofeveryday

eelingof confidencehasreceivedarude

eredonebyonethe mysteriesandparadoxes

tumtheoryof thepresentday.

ntheconceptionofmatteras acon-

acedbytheconceptionofdiscretequanta

beginningto seethatthiswasbut thefirst

nagainstthetheoryofthecontinuum.Step

edto"quantize"physico-chemicalphenomena.

go, andhowmuchofourformerbelief

will remain,wecannotnowpredict;but

manyofourbestestablishedprinciplesof

wemaybe surethatthetheoryof atomsis

thecomingtheoryofdiscontinuityinnature.

icbeliefwhichatall timeshasbeen

eathatallof thevarioussubstancesknown

manifestationsofa singlebasicsubstance.

entificimplicationsoftheatomictheory,so

escientificconsequenceofthetheoryof the

of theseveralatomsappearedtobe

ydrogen,andadvancedtheidea thatall

dofhydrogenatoms.Thisproposal,which

,receivedtheadherenceofsomeofthebest

perimentalevidencewasconflicting.

butroughlydetermined,andwhileaccidental

veragebringatomicweightsnearertowhole


/ h t t p : / / w w w . h



16/169

ndencytowardtheroundingoffofuncertain

toaccountfortherulediscoveredbyProut.

ethodledtoanincreasingaccuracyin

overacenturythe determinationofatomic

e favoriteoccupationsofchemists.Itsoon

atomicweightsingeneralwerenotexact

en,andFront'stheorygraduallyfell into

wasoccasionallypointedoutthatthe

sweremuchnearertowholenumbersthan

elawsofchance.

97)showedthatthechanceofthe

wenty-twoelementsfallingasnearto

wouldbe lessthanonein onebillion.It

abletoascribethecloseapproximationofatomic

,nottopure chance,butrathertosomesuch

hatofProut,perhapsmodifiedbysome

ure.Indeedwearenownearly convinced

rect,andthatthe deviationsofatomic

bersaredueto twoseparatecauses.

as foreseeninaremarkableprophecy

.Hesays:"Couldone not,forexample,

mentalprincipleofthislaw(of Prout)

sition,towhichIdonot attachimportance

thatonemight explainthediscordance

weentheresultsof observationandthe

ofthisprinciple?Might onenotsupposethat

wnbutprobablydiffersfromthe physical

atwerecognize,andwhichhasdetermined

omsofthe singleprimordialmattertogive

calatoms,andtoimposeuponeachofthese

randparticularproperties,hasalsobeenable

ponthewayin whichthesegroupsofatoms

ttraction,suchthatthe weightofeachof

m oftheweightsofthe primordialatoms

incetheadventofrelativityweknowthat

withitsenergy,sothat iftwoatomscombine

energythereis aproportionallossinmass.

orthedeviationsfromthe ruleofProut.

enowrecognizeasresponsibleforsome

mthe ruleofProutis thatmanyofthe

neormore isotopeswhichcanbesepa-

tdifficulty.Suchelementshaveatomic

therelativeamountsofthe severalisotopes

eparateisotopes,studiedbythemethodof

opedbyJ.J. Thomson(1913)andby

part showatomicweightswhicharevery

one whichconcernswhatisnowcalled


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17/169


dit wouldcarryustoofar fromthemain

scussinanydetailthemanyimportant

ernthestructureandthedisintegrationofthat

ity.

sonelectricityit wasfoundthatdifferent

ontactandthenseparated,remaincharged,

ther withresinouselectricity,orinFrank-

ositiveandnegativeelectricity.Different

xercisedifferentdegreesofattractionforthe

ntexperimentsofDavy(1807)concern-

riccurrentuponvariouschemicals,hewas

ticlesofsubstancesbecomeelectrifiedwhen

les,andthattheattractionbetweentheoppo-

isthecauseof chemicalunion.Thisidea

us(1819)intotheelectrochemicaltheory,

yearsthedominanttheoryofchemistry.

wereexplainedinaccordancewith

onsidered,whenanatomofzinccomesin

ygen,thataflow ofelectricityoccurswhich

andthelatter negative.Althoughsulfur

wardzincit ispositivetowardoxygenand

ofamoleculesuchas sulfurtrioxide.Thus

coxideandsulfurtrioxide,wasregarded

ectricforcesoperatingbetweentheoppositely

womoleculeswhenbroughttogetherwould

ncoxideasa wholebeingpositivewith

hesetwomoleculeswouldinturn beheld

stoproduceamoleculeofzincsulfate.Soon

oapplynot onlytosimplecompoundsbut

bodiesknowntomineralogy.

lordualistictheorywasfirstproposedit

ofthe firmestchemicalcompoundsarecom-

H2 orN2.Theexistenceofsuchtypesof

entlyinsuperableobjectiontothetheory.

hemistrydrewattentiontoa classofcom-

tinadequatelyintothedualisticschemeof

spointedoutthatelectronegativechlorine

ectropositivehydrogen,innumerouscom-

gtoproduceanypronouncedchangeinprop-

hesediscoveriesthedualistictheorywas

evelopmentofstructuralorganicchem-

ule(1858) onthechemicalbondandonthe

eatoms,totheworkof LeBel(1875)and

eoisomerism.Nogeneralizationofscience,


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pableofexactmathematicalstatement,has

ccessinassemblinginsimpleform amultitude

ationsthanthisgroupofideaswhichwecall

phicalformulaisfarmorethana mere

ments;ithasbecomearemarkableshorthand

reatvarietyofchemicalknowledge.

structuralchemistrytheelectrochemical

seemedtoplaybut asubordinaterole.But,

husiasmforthe synthesisandanalysisof

ceswasspent,attentiononcemorerevertedto

pe.Faraday(1833)hadshownthatthe

eproportionsis validnotonlyforthe

oforelectricity.Thusagramofcopper

electricityinthe electrolysisofacupricsalt

uproussalt.Itis singularthatsomany

nouncementofFaraday'slawbeforeitwas

esa discontinuityofelectricityinthesame

mplieda discontinuousstructureofordinary

ningelectricityoccursinquantathatare

mbiningwithatomsandgroups ofatomsonly

sHelmholtzin hiscelebratedFaraday

intedout thisdeductionoftheatomof

alled,theelectron.

mofnegativeelectricity,theelectron,is

investigationsofJ.J.Thomsonandof those

proofthat freeelectricityisnegativeelec-

oftheratiobetweenthechargeand themass

y ofthephysicalandchemicaleffectspro-

s,compriseoneofthemostfascinatingchap-

ceswasgreatlyfosteredby theelectro-

Arrhenius(1887)whichclarifiedinso

deasconcerningsaltsolutions.Thistheory

ticismhasfullyjustified itsessential

vincedthat,inadiluteaqueoussolutionof

separatedinto twodistinctparts,oneof

ge,equaltothe chargeofanelectron,while

gedin equalamount.Thuswehavefull

menonwhichwasassumedinthedualistic

ptedtoreverttothe electrochemicaltheory

micalunion,andagain theymetthediffi-

meansthepropertiesof substanceslike

drogen.Thereobviouslyisawidegapbetween

handan extremely"polar"substancelike

presumablythereisatall timesaconsiderable

yfromthesodiumtothechlorine,andwhich

ssociatesintosodiumandchlorideions; on

P u b l i c D o m a i n ,

G o o g l e - d

i g i t i z e d

/ h t t p : / / w w w . h

a t h i t r u s t . o r g / a c c e s s

_ u s e # p d - g

o o g l e


19/169


non-polarsubstancelikediatomichydrogen

sonfor,norshowsanyevidenceof,such

stweconcludethattherearetwodistinct

neacompletelypolarandthe otheracom-

dmustweassumethata substancewhich

ateproperties,andtobeslightly polarized

xtureofpolarand non-polarmolecules?

sof ascribingallthemostvariedtypesof

thesamefundamentalcause,differingonly

ofitsmanifestation?Thesearequestions

ntioninlaterchapters.


G o o g l e - d

i g i t i z e d

/ h t t p : / / w w w . h


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o o g l e


20/169

hemist's

heatomictheoryit wasknownthat

groupsorfamilies,and assoonasDalton's

ecameamatterofi nteresttoseewhat

eenthepropertiesofsimilaratoms and

utthesametimethatProut announcedthe

chanimpetustotheaccuratedeterminationof

overedbyDobereiner(1816)thatin a

edelementstheatomicweightof acertain

proximatelythemeanof theatomicweights

knowmanyoftheelements,whichhe

sotopes,andyet thesecoincidencespointed

evidentinourpresenttableof atomic

t beenexplained.

weentheatomicweightsandtheproper-

ardlybe discoveredduringtheperiodin

reassignedatomicweightswhichweremulti-

irtrue values,butaftertheintroductionof

micweightsbyCannizzaro(1858)many

suchperiodicrelations.Probablythefirst

present periodictablewasdeChancourtois

elementsina spiralintheorder oftheir

ethesignificantremark,"Thepropertiesof

tiesofnumbers."Similarobservationswere

andmorefullyby LotharMeyer(1870),

69)thatweowethefullest recognitionof

onsequences.Itis unnecessarytorecitehere

eriodiclawofMendeleeff,whichforfifty

principleof systematicchemistry.Thecon-

snot shakenbutratherstrengthenedbythe

newfamilyoftheelements,thegasesof the

entiontoacertainerror intheoriginal

Theideathatthe propertiesoftheele-

annerwiththeatomicweightsisuntenable,

snoquantitativerelationshavebeenfound

htofanelementandits chemicalproperties.


/ h t t p : / / w w w . h



21/169


ftheelementswesee thatthereisa difference

ghtbetweensulfurandchlorine,whilethereis

weenseleniumandbromine.It istherefore

ofindthat iodinehasanatomicweightactually

e elementsweretobearrangedstrictly

atomicweights,iodinewouldbeforcedinto

lfur,while telluriumwouldfallamongthe

nes.

onsofargon andpotassiumandofcobalt

ed.

4)whofirst comprehendedtheunder-

classification.Thepropertiesofanelement

"independentvariable"whichisnot,how-

thesecondofhis remarkablepapersin

rdinalnumberofeachelement,hewas

exactplacingof alltheelementsoftherare

felementsstill remainingundiscovered,and

hesevacanciesinthe periodictable.In

e wascompletelysuccessful,andhistable

calwithour presenttableofatomicnum-

medtheexistenceoftwoelementsbetween

ereduceallof hisnumbers,exceptthe


/ h t t p : / / w w w . h



22/169

MIST'SPICTUREOFTHEATOM25

Europium63

nium64

bium.*.65

ysprosium66

m67

um68

ulium69

bium70

tecium71

Tantalum73

sten74

4475

mium76

46Iridium77

m78

old79

ry80

m81

ead82

Bismuth83

nium84

iton86

87

um88

59Thorium90

91


/ h t t p : / / w w w . h



23/169


accompanyingtable,whichgivestheatomic

pted.

gattackedbythephysicists.Rutherford

xperimentsonthereboundingofalphaparticles

udethattherelies inthecenterofeachatom

tivechargewhichcanbe neutralizedby

numberof negativeelectrons.Itwas

k(1913)thatthe integralnumberwhich

argeonthenucleusof anatomrepresentsalso

ndX-RayFrequency.

determinesthepositionofthe elementinthe

sharp reliefbytheextraordinaryresults

eley(1913,1914)onthe X-rayspectraof

eleyfoundthatwhenthevariouselements

nsinanX-raytube eachelementemitsa

omposedofanumberof highfrequencylines.

groups whichappeartobeidenticalinform

exceptthattheyareshiftedstepby stepwith

igureIshowsthe wavelengthsofapair

uency,theKaandK^lines,of theelements

e,rubidiumandstrontium.Theevidentgap

diumshowsamissingelement,whichinthis

theelementkryptonwhichcannotbemade

e.

onof anyonelinechangesfrom

wnin Figure2,inwhichtheatomicnumbers

againstthe squarerootofthefrequency


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24/169


thepointsfalling,withintheverysmall

r,uponacontinuouscurvewhichis nearly

mbers,Rydbergconcludedthatthere

oup beginningwithcesiumandendingwith

ensupposedthata largernumber,probably

period.Thisnewconclusion,whichis

kofMoseley,led Rydbergtoasimpte

ecalledtheruleof "quadraticgroups."Since

oftwounknownelementsbetweenhydrogen

eelementsin thefollowingperiods:

e,8; Na—A,8;K—Kr, 18;

?)— (?),32.Thisgives twoperiodsof

twoof 32,andthenumbers2,8, 18,32

2, 2X 32and2X 42-

tionablywronginassumingthetwo

thoseofhydrogenandhelium.Thisseems

edbytherelationsbetweenthe spectrumof

edspectrumofhelium,whichweshalldis-

oreover,althoughonlyafew members

ementsareknown,thefirstpart ofthis

analogoustotheperiodof32 justpreced-

resemblancetothe periodbeforethat,which

ismorelikezirconiumthan likecerium,

emberofthelast period,belongsdefinitely

ybdenum(whichisthesixthmemberofthe

mstobearnoresemblancetoneodymium

rofthe periodof32).Whilethereforethe

ydberg'stheoryinfull,neverthelessweshall

quadraticnumbersplaysanimportantrole

omicstructure.

sentialfeaturesoftheperiodicclassifica-

pertiesof theelementsareperiodicfunc-

rs,(b)Whenthe elementsarearranged

intoone periodof2elements,twoperiods

nda fragmentaryperiodwhichasfaras

mbleaperiodof18.(c) Elementswhich

sitionsintheseveralperiodshavesimilar

beenmadetoexpresstheperiodicrelation-

eformofatable, adiagram,oraspace

beregardedas thoroughlysatisfactory.

terestingrelationshipswhichexist,others

erelyformalrelationships.Onthewholeit

mple tablewhichtellslessthanthe whole

cha table,forwhichIamlargelyindebted

below.It bringsouttheessentialrelations

houghnotalltheinterestingones.


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siumtozinc isnotclearlyindicated,and

ellbeplacedabovelithiumasabovethe

matterto whichweshallrecur.

asattemptingtoexplainto anele-

ysomeoftheideasinvolvedin theperiodic

nthenewtheoryofthe electron,andcom-

whichareimpliedintheperiodicclassifica-

einnerstructureofthe atomwhich,

dumof1902.

aincrudities,Ihaveeversinceregardedas

hearrangementofelectronsintheatom.In

rtion ofmymemorandumofMarch28,

theory.

eoryof atomicstructureareasfollows:

omarearrangedinconcentriccubes.


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helementcontainsonemoreelectron

eelementnextpreceding.

sisreachedintheatomsof therare

mesinsomesensethe kernelaboutwhichthe

thenext periodisbuilt.

er incompletecubemaybegivento

,orenoughelectronsmaybe takenfromother

be,asin Cl~,thusaccountingfor"positiveand

aofMendeleeff,thathydrogenisthe

od,Ierroneouslyassumedheliumtohavea

gardingthedispositionofthe positive

eelectronsintheneutralatom,myideaswere

nedat thattimetowardtheideathat the

adeupofdiscreteparticles,the localization

calizationoftheelectrons.

ngthearrangementofelectronsinthe

ussedfreelywithmycolleaguesandinmy

herpublicity.Indeedwhilethistheoryof

aremarkablysimpleandsatisfactoryexplana-

ccurswhensodiumcombineswithchlorine

did notseemtoexplainchemicalcombina-

uchasoccurinthe hydrocarbons.

lftobelieveintwodistinct kindsof

ratherthattheunionof sodiumandchlorine

and carbonmustrepresentextremetypesof

whichultimatelywouldbefoundtobe com-

ounds.However,itwasmanyyearsbefore

cilethisideaentirelywiththe ideaofthe

recognizedthestabilityofthe group

begg(1904),whosepaperon "Valence

AttemptataTheoryof MolecularCom-

ificantremark,"Thesum8of ournormal

essesthereforesimplesignificanceasthenum-

esentsthe pointsofattackofelectrons;

ositivevalenceindicateshowmanyofthe

d electronsinordertomakethe element

butiontotheinterpretationofthe periodic

mson(1904)whoconsideredthemathe-

eassumptionthat theatomsoftheelements

trons"enclosedina sphereofuniform

ewasthusledtoconcludethataring of

andrevolvingaboutapositivecenter,would

rofelectronsinthering exceededacertain

reakintotwoconcentricrings.Thus,if the

outer ringisincreased,alimitis reached


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28/169


ed,andso on.Asanillustrationof the

eshowedthatif anumberofsmallmagnets

surfaceofwater,sothatallof thenorth

he southpoleofalarger magnetisbrought

magnetswillorient themselvesaboutthe

gs.Thomsonrecognizedthatundercertain

ouldarrangethemselvesnotinrings ina

dralfiguresaboutthe center,butthedifficulty

oninsuchcasesledhimtorestricthis atten-

a singleplane,andthisdecisionmayhave

rsomelatertheorieswhichassumea co-planar

natoms.

ytheanalogybetweenhisarrangementof

systemofMendeleeff."Thusifweconsider

sol'corpuscles(electrons)havingonthe

constantnumberof corpuscles,wehave,at

temswhichbehaveliketheatomsof an

ncapableofretainingachargeofeither

city;then(proceedingintheorderof increas-

wehavefirsta systemwhichbehaveslike

electropositiveelement,nextonewhich

divalentelectropositiveelement,whileat

swehaveasystemwhichbehaveslikean atom

telyprecedingthis,onewhichbehaveslikethe

tronegativeelement,whilethisagainis

gliketheatomof adivalentelectronegative

esisverylikethat observedinthecase

nts.Thuswehavetheseriesofelements:

n eachoftheseserieshasno valency,

telectropositiveelement,thelastbutone

gativeelement,thethirdisa divalentelectro-

buttwoa divalentelectronegativeelement,

tronegativeones,inwhichthecorpuscles

withatomslike theelectropositiveones,in

otnearlysofirmlyheld, theforcestowhich

bytheactionof theatomsuponeachother

entofcorpusclesfromtheelectropositive

cetotheelectronegative.Theelectro-

eta chargeofnegativeelectricity,theelec-

ositive,theoppositelychargedatomswill

hemicalcompoundoftheelectropositiveand

lbeformed."

n'spictureoftheunionoftwoatoms


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eofferedbyAbegg,althoughunlikethe

dhisresultsaspartlydeduciblefromcertain

ngtohisassumptionofa sphereofpositive

eelectronsweresupposedtobeimbedded.

positivepart oftheatomsoonprovedto

sstudyofthescatteringofalpharays by

sexplicableonlyontheassumptionthatthe

concentratedinaverysmallregionat the

eforeproposedwhatmaybecalledthe

cstructure,accordingtowhichtheelectrons

vinginorbits aboutthesmallpositivenucleus,

ws offorce(theinversesquarelaw)that

planetsabout thesun.Thistheoryofthe

herdiscussedinthe nextchapter.

veryinterestingpaperentitled"A

ructureoftheAtom."Herethe electron

ring ofnegativeelectricitywhichtherefore

ment1andcouldbecalledamagneton.As

ectronsormagnetonswereassumedtolie

iformpositiveelectrification,andParson

cforcesbetweenthemagnetonswouldcause

esincubes(notconcentric,butlyingalong-

gepositivesphere).

rson'stheorywhichisnowgenerally

dforwhichI amafraidthatIam inpart

sonfirstshowedmehismagnetontheory

ectricitycapableofvariousdegreesof

exceedingthevelocityoflight.It wasat

butedafixed magneticmomenttohis

inasensethe elementaryunitofmagnetism

unitofelectriccharge.Thisidea hasnot

sunlikely,althoughperhapsnotimpossible,

sanymagneticpropertiesexceptwhenit

molecule.Itis,however,tobeobserved

hichweshalldiscussinthenext chapter,and

ctorypictureofthemotionof electrons

n'stheory,thereappearsagaina definite

ydevotedtoadiscussionof thestability

tronsandthetendencytoformsuchgroups

alunion,andhe showedthatthosecom-

mpletegroupsofeightcannotbe assumed

eticpropertiesshowthatthe moleculepossesses

.

thereappearedtwopapers,oneby

eofthe elementaryprinciplesofmagnetismwill

ter.


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ungalsFragedesAtombaus,"andoneby

heMolecule."Thesetwopapersoffered

thestructureofthe atomsandofthose

arsort,whereeachatommaybe regarded

nion.In bothpaperstheelectronsof

surroundingthesmall positivenucleusin

tbeingagroupof two,thesecondagroup

ofeight,andthenother groupsofsome-

cter,butalwaysendinginanoutergroup

tomsoftheraregases,as alsoinsimple

cessivegroupstooccurinconcentricrings

n accordancewithmyearlyviewsex-

ArgonAtom.

edthesegroups toconstituteconcentric

ensionalstructureaboutthecentralatom.

uresof theargonatomsidebyside.

ngroupswere supposedtoreachthe

ryandstabilityinthe atomsoftheseveral

group oftwo,neonwithitsgroups oftwo

roupsoftwo,eightandeight,and soon.

vedashavingastrongtendencyeithertogive

electronsinsuchmannerastoape the

egas.

sizedthepeculiarityofhydrogenwhich,

anbecomethesimplestof positiveions,

micnucleus,whilebytakingon oneelectron

oftwo, characteristicoftheheliumatom'.

arlylikethe takingonofoneelectronby

rm F~orCl~,withstructurescorresponding

eltjustifiedinregardinghydrogenas

tleast,to thehalogens;andthereforepre-

drideswouldprovetohave thecharacter


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lionand hydrideion,andfurtherthat

ouldproducehydrogenatthe anode.This

yverifiedinthe workofBardwell(1922)

ysingameltcontainingcalciumhydride,and

anodeinamountcorrespondingtoFaraday's

tomsshowa verymarkedtendencyto

htelectrons,andthistendencyfurnishesa

ofalargeclass ofthemorepolarchemical

heseveralpapersofParson,Kossel and

therandattemptedtofurnishan equally

poundsofthelesspolartype,but thiswill

apter.


G o o g l e - d

i g i t i z e d

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o o g l e


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ysicist'sViewofthe Atom.

temittedorabsorbedby asubstancewas

othatsubstance,thestudy ofcharacteristic

eimportantmethodsofchemicalanalysis.It

(1860,1861)whoshowedthegreatpower

yin thedetectionofexistingelements,

ofnewelements.Theheavyalkalimetals,

ethusdiscoveredbythem.

sareplacedina flamethebrightspectral

eemordinarilytobe characteristicofthe

articularcompoundwhichisused.Ithas

thevariousemissionspectra,whetherfrom

be,or flame,fallintotwoclasses,which

nespectraandbandspectra,andthere has

ontheview,firstsuggestedby Helmholtz,

aare characteristicofmolecules,theline

hichhavebeen setfreeunderthecondi-

eemissionoflight.

haracteristicspectrallinesoftheele-

ystudied,andwhosewavelengthscanbe

acywhichishardlyattainedinanyother type

urement,shouldfurnishinformationofgreat

rstructureandbehavioroftheatom.But

nbeutilizedwemust havesometheoryof

mittedorabsorbedbyasubstance.

ghtstrengthenedtheanalogybetween

omaticlightischaracterizedbyitsfre-

stasa musicaltoneischaracterizedby

gthinair. Theemissionofamusicaltone

s vibrating,likeatuningfork.So,ac-

llthe classicaltheoryoflightemission,light

omethingwithinthemoleculeoratom,and

ell'selectromagnetictheory,itwasassumed

ngcarriedanelectriccharge.

theorytheelementaryvibratorsorres-

awsofelasticbodies andthuspossessa

d,independentoftheamplitudeofvibra-

mall.Thesevibrators,setinmotionby


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cdischarge,arethenthe sourceoflight;

htspectrallineisdue tothepreponderance

meonenaturalfrequency.

suponasubstancecontainingsuch

posedto acquireenergyofvibrationatthe

speciallyofthat partofthelight whichhas

gtothenaturalfrequencyofthevibrators.

sacquiredis thenconvertedintothermal

ltheoryof lightabsorption.

sionand absorptionoflightthrough

rtsofthe moleculeoratomhasfurnished

ationofalargenumberof phenomena.It

etthat wenowfindourselvesobligedto

wholly,thissimple pictureoftheinter-

dlight.

equacyoftheclassicaltheoryisfurnished

trallinesingroups orseries.Nowbyanalogy

atsendsout aseriesoftonesand over-

edthattheelementaryvibrators,especially

uenceoneuponanother,mightemitnot

nes,andthe discoverythatasingleelement

spectrallinesseemedatfirstto support

uantitativerelationbetweenthefrequencies

ementaryspectrumprovedtobeverydiffer-

sto beexpectedfromtheanalogytomusical

ssina simplenumericalformulathe

ectralserieswereunsuccessfuluntilBalmer

portanthydrogenseriesa formulawhich

rototypeofallformulaeforseriesofline

lmer,althoughcontainingbutasingle

ucedwithmarvellousaccuracythepositions

enseriesastheyhad beenobserved,not

lso inthespectrumofsun andstars.

esoflinesby theformula

andnisany oneofthewholeseriesof

integralvaluethuscorrespondstoasingle

whichthelinesbecomecloseras nincreases,

valueknownas theheadoftheseries, where

ne(in reciprocalseconds)isequalto

ationmaybewritten


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34/169

YSICIST'SVIEWOFTHEATOM37.

methodsofspectroscopyhavegreatlyin-

edeterminationofspectral lines.Twenty

ave beenobtainedinthelaboratoryand

tion,andthefrequenciesofthese linesdo

omthose calculatedfromtheformulaby

llion.

discoveriesrelating tospectralseries

97)inobservingthe spectrumofthestar

found,everyalternatelineof whichap-

ineoftheBalmerseries.The wholeseries

edbytheformula

nticalwiththose oftheBalmerformula

vesthe additionallinesofthePickering

Thesenewlineswere originallyascribed

arform,but weshallseethatBohr has

etohelium,andthe similaritybetweenthe

sthusfurnishesa remarkableillustration

onshipbetweenthelinespectraof different

eataccumulationofexactspectroscopic

adled tothediscoveryofonlytwo funda-

othofwhichweremadebyRydberg(1890),

citywehavealreadyrecognizedinhisdis-

fthe atomicnumbers.

a certainnumberappearedinthe

rthelinespectraof anumberofelements.

announcedas"a constantcommontoall

,"isnowrecognizedasauniversalconstant

onstantofRydberg(exceptfor avery

fficientwhich appearsinthesecondmember

tgeneralizationofRydberghasbecome

principle.Whenanelementexhibitstwo

s,the linesofoneseriesand thoseof

tooneanother.According tothecombina^

suallystated,thefrequencyofeach of

ainedfromthe sameatomicspeciesmay

everaldifferencesbetweenarelativelysmall


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35/169


es.Inordertoillustrate thispointwemay

ectrumofmonatomichydrogen.

seriesthereareanumberof otherim-

hareascribedtofree hydrogenatoms.One

obtainedbyLyman(1904,1906)in the

schen(1909)intheultra-red,andvery

ourthserieshavebeenobtainedbyBrackett

-red.Theformula:whichreproducethe

s:

,

riesarerepresentedinFigure5, whereonly

eriesareshown(togetherwiththe head

bya dottedline).

Series.

eofany oneoftheseseriesmaybe

feverylinecanberegardedas thedifference

hebasic frequencies

Balmerseriesisv2* — v4*,thethirdline

— v4*,andthefirst lineofthePaschen

he combinationprinciplegraphically

nfrequenciesareplottedfromlefttoright.

tthevaluesof v*,thebasicfrequencies,

zontallinesterminatingatthesevertical

nciesofthreespectrallinesthat wehave


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36/169

HYSICIST'SVIEWOFTHEATOM39

mentsthanhydrogenwefindacondi-

ity.Asarule itisno longerpossibleto

ciesoftheserieslines, orthebasicfrequen-

rmulaeassufficedin thecaseofhydrogen.

beenmostusefulinexpressingthese series

onstants,andappeartobeof onlyapproxi-

sswefindalsointhesemore complexcases

ciesareoncemoreobtainableasexact

esofHydrogen.

ainbasicfrequencies,incompleteaccordance

ciple.

tedwithRydberg,havebecomethe

spectralserieswhichhas beensorapidly

decade.Beforediscussingtheserecent

arytogivebrief considerationtothatrevolu-

hichisknownas thequantumtheory.

tdeductionsofthekinetictheoryofgases

ses shouldpossessthesameaveragekinetic

ven temperature.Thisideawascarried

nd solids,anditwasassumedthat every

meaveragekineticenergyata giventempera-

LawoftheEquipartitionofEnergy.

nntotheexplanationofthe lawof

omsofasolidpossessthe samekinetic

monatomicgas,andiftheyvibrateabout

ncewithHooke'slaw,sothat(asin the

n)theaveragepotentialenergyequalsthe

enthetotalthermalenergyofthe atoms

sgreatasthat ofanequalnumberof

;andtheenergywouldincreasetwiceas

refortheformeras forthelatter.But

nlytrueasa limitinglawathightempera-

ordinarytemperaturesandallsubstances

averymuchsmallerchangeof energy

thatlawrequires.If weplottheenergy

erature,asinFigure7, thedottedlineex-


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37/169


aw,whilethe behaviorofanactualsub-

ontinuouscurve,whichhasthesameslope

ightemperatures.

appearstogivea verysatisfactory

energyofamonatomicgas.Butthe atom

nstheultimateparticle.Bythe equiparti-

particleswhichcomposesuchanatom

energy.Onthe contrarywearecon-

asacquiresnoappreciablethermalenergy

opper.

thetranslationalmotionofitsmolecule

sityoftheequipartitionlaw,itneverthe-

onsequenceofacceptedmechanicalprinciples.

mtheseprinciplesbythemethodsof statistical

nmadeinamannerentirelyfree fromob-

believedthatsuchadeductionispossible.

erencethatthemechanicsofatomsdiffer

nownmechanicsofmassivebodies.

notonlyin itsapplicationtothethermal

butalsowhenit isappliedtothe distribu-

trumofradiationemittedbyablackbody.

mablyhavelightof allfrequenciesfrom

y speakoftheamountofradiantenergy

entwochosenfrequenciesY!andv2.It

900)tobe aconsequenceoftheequipartition

sedbetweentwosuchfixedlimitsof fre-

naltotheabsolutetemperature,asshown

e8.Thecontinuouscurveofthatfigure

sasbroughtoutby Wien(1896)andmore


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38/169


scurveapproachesastraightline,as

titionlaw,onlyathightemperatures.

ationforthedistribution ofradianten-

hthedeductionsfromacceptedmechanics

nouncedahypothesisofunusualboldness

assofnewlawsand hypotheseswhichhave

sthequantumtheory.Planckassumed

odiescontainelectricaloscillatorswhich

n,notin acontinuousmanner,butbyfinite

tEnergy(BetweenTwoGivenFrequencies).

thesefiniteamountsof energyispropor-

ncyofthe oscillator.Hefurtherassumed

obethesamefor alloscillatorsandthere-

whichisdenotedbyh andknownasthe

ngtothis theory,anoscillatorwhosenatural

energyonlyin theamounth\orsome

thatwegofurther,and regardthe

scillator,asa quantumorcorpuscleof

servingacertaindegreeofindividuality,

sa whole.Thisideahasnotbeenwidely

ifficultyofitsreconciliationwiththephe-


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39/169


ceoflight.However,itledEinstein to

deductionsfromquantumtheory,namely,

.Accordingtothisequation,whenasub-

ochromaticlightoffrequencyv,themaxi-

acquiredbyoneof itselectronsish\.

awtheconnectionbetweenthetwotypes

partitionlaw,ofwhichwehavespoken.If

obecomposedofatomswhichareanalogous

torsofPlanck,andthereforecapableof

iteincrements,theenergywouldnotbe

mperaturerequiredby thelawofDulong

uresmanyatomswouldbeunableto acquire

rewouldpossessnoenergy atall.Thus,

ormula,Einsteinobtainedhisequationfor

whichqualitatively,althoughnotquantita-

numerousmeasurementsofspecificheats

eatlow temperatures.

quantumtheoryProfessorEinsteinre-

ntumtheorywas notreallyanewtheory,

fthefalsity ofprevioustheories.This

escientistshavebeeninclinedtogiveup

sthelawsofconservationofmomentum

cethemby analogoustheoremswhichare

ense.Othershavegonesofaras tocon-

ofspaceandof timemustbereplacedbya

nlyconcludethatin givingupthecon-

ndreplacingitby thetheoryofdiscrete

ms(orelectronsandnuclei),wehavesome-

Aracewithmorelimitedsenseperceptions

he propertiesofsandandconcludethese

eexistenceofgrains,butwouldtheythen

e grainsascomposedofsand?Yetthis

atmodernsciencehassanctioned.Theprop-

eenexplainedbyassumingitto becom-

hichwenaivelyconsidertheelectronsas

speculateconcerningthedistributionof

roncenter.Wealsohaveregardedtheatoms

milartothoseof thelargerbodieswhich

sphenomenawhicharegroupedunderthe

the newdatainthelight ofwhichwe

ometryandthenewmechanicswhichare

nityofelectronsandnuclei.Quantum

forfurnishingnoadequatemechanism,but

presentproblemlies deeperthanthis,

nymechanismbasedonourexistingmodes

e explanationofthemanynewphenomena

mis disclosing.


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40/169

HYSICISTSVIEWOFTHEATOM43

r'sTheory.

scopywithitsscarcityof guiding

ceofalmostuncorrelateddata,orderand

atasinglestrokethroughthe brillianttheory

Tothistheory,whichhas sojustlycap-

ists,wemustnowgive ourattention.It

heHydrogenAtom.

ewhatdifferentmannerfromthatemployed

norderto separatethatpartofthetheory

pendentlyofanyatomicmodelfromthepart

.

aseofanatomlike monatomichydrogen,

ofanucleusandone electron,itisfirst

onmayassumeanyoneof awholeseries

e maybespokenofasan energylevel.Thus


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enttheselevelsbyaseries oflines,such

twolinesis equaltotheenergydifference

ocorrespondingstates.The lowestlevel

ergyandthereforethemoststable state

eseries,and theenergyatthelimit

thedottedline)is assumedtorepresent

henthe nucleusandtheelectronare com-

eanother.Thedifferencebetweenthe

dthislimitingenergycanbe designatedby

.Forconvenience,thevalueofthelimiting

ro,and wemaythensaythatthe energy

of thesecondlevel£2*,andso on.All

ownegative.

adebyBohristhat theenergyatany

ePlanckconstant,gives thenegativeof

frequencieswhichwehavediscussedin a

mwhichthevariousspectral linesofthe

Inotherwords,it isassumedthat

tthe atomemitslightonlywhenthe

lto another(orabsorbslightonlywhen

oneleveltoanother).Theenergyof the

edifferencebetweentheenergiesofthetwo

fthelight isthisenergydifferencedivided

almerseries,whichisv2* — v4*,issupposed

ectron fallsfromthefourthto thesec-

ydrogen,andtheotherlinesofthe Balmer

nelectrondrops fromtheseveralupper

while thelinesoftheLymanseries are

ndropsfromvariouslevelsto thefirstand

tothe complexspectraoftheelements

thisbriefsummary,itis impossibletoshow

tothe significanceofspectralseriesis

.Nordoesthis partialstatementofhis

thatbrilliantgeneralization,forwhenwe

delweshallsee thatanequallysimple

morefar-reachingconclusionsthan can

tionswhichwehaveso fardiscussed.

t thetheoryaswehavedevelopedit

sentialelementsofthequantumtheory.The


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42/169


tomiclightoffrequencyvcanchangethe

e amounth\.ThesecondisPlanck's

nismintheatomwhoseenergycanvary,not

niteincrements.

ySpectra.

explainsthelongfamiliardataof

htmodificationgivesanequallysatisfac-

ewerdatarelatingto X-rayspectra.Let

ntwhoseatomcontainsalarge numberof

ncemorethattherearecertainenergylevels,

e Klevel,thenextthe Llevel,thenext

maynextassumethatonly alimited

epresentateach oftheselevels.Instead

sasa mereframework,aswedoincon-

ogen,wemayassumethateachof the

elowerlevels—containsitsfullquota of

meansanelectronfrom theKlevelis

nelectronfromthe Llevelmayfallin

g risetothespectralline designatedas

theM levelwhichfallsintothevacant

eK'0,andelectronsdroppingfrom higher

eswhich,ifthespectroscopicresolutionis

rvedasa singleline,K7.Soalso an

omtheLlevel,and ifitsplaceis filled

leveltheLalineresults, andsoon,forthe

utifulexplanationofthepeculiarab-

otfind, asinthecaseof ordinaryspectra,

escorrespondingtotheseveralemission

aysatthe frequencyK,,wouldindicate

redfromtheK leveltotheLl evel,butin

elalreadyhasitsquotaof electrons,andthis

sible.Absorptioncannotbeginuntilthe

ufficienttoremovetheelectronentirely

tooneofthe outerlevelswhichhasnot

Theobservedfactisthatacontinuous

sfromthehigherfrequenciesdowntoa

ancorrespondstothe KTlineandthere

velindifferentelementsis supposed

hechargeof thenucleus,wehaveanew

erelationbetweentheX-rayspectraand

Moseleydiscovered,andwhichhasbeen

pterII).

sbeenofthegreatestservicein account-

eristicsofX-rays,althoughhereas with


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43/169


rearecertaincomplexities,adiscussionof

rafield.The conceptofenergylevels

tionprinciple,whichprovedsousefulin

aryspectra,shouldholdforX-rayspectra

determinedbytheenergydifference

ls,andtheKaline bythedifferencebetween

eLalineis determinedbythedifference

,the frequencyoftheKalineshould

thefrequenciesoftheothertwo,and this

Potentials.

electronsemittedbyahotcathode

adientto ananode,theelectronsacquirea

dingtothedifferenceinpotentialbetweenthe

whencertaingasesareintroducedintothe

ghmeetingandreboundingfromthegas

n anelasticmanner,andfinallyarriveat

neticenergywhichtheywouldacquirein

sis farfrombeingtrueof allgases,but

esecollisionsbetweenelectronsandmole-

telyelasticwithinthelimits ofexperimental

otionof theelectronthroughthegas

ess.

type,ifthepotentialdifferencebetween

uallyincreased,adefinitepointis reached

entlylosesenergyuponcollision.Wemay

electronreboundsfromthemoleculeelastically,

nergyof theelectronreachesacertain

isgivenupto themoleculeoncollision.This

stmadebyFranckandHerz(1913),has

vestigations.

electronisincreasedbeyondthisfirst

otherpointsbecomemanifest,whichindicate

eenergyoftheelectronis giventosome

Thefirstofthesecriticalpointsto be

edwiththesuddenemissionoflight. The

t ofoneofthecharacteristicspectrallines

hichsufficesto producethisinelasticcol-

htemission,isknownasaresonancepotential.

ghest ofthesecriticalpotentialsisfound

uddenappearanceofgaseousionization.

eelectronstrikingthe moleculeknocks

atthetwoelectronsdepartingleavebehind

heminimumpotentialrequiredtoproduce

nastheionizationpotential.

emelysatisfactoryqualitativeandquan-


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sephenomena.Ifweconsideranatom

oststableposition,thatis,uponthe lowest

eatomcanonlyacquireenergyifenough

ectrontooneofthehigher energylevels.

byanelectronwhichhasinsufficientenergy

collisionmustbeelastic.Ontheother

ectronpossessesjustenoughenergyto raise

mtothe nextenergylevel,itmaylose

the collisionisinelastic,andtheelectron

e secondlevel,orresonated,mayamoment

level,emittingthefirstline oftheelement's

evelocityofthebombardingelectronmay

he electronoftheatomtopass throughthe

elsandbecomeseparatedaltogetherfrom

becomesionized.Suchisthequalitative

andionization.

ionisequallysatisfactory.Theenergy

ncemustbe equaltohtimes thefrequency

tralseries.Theenergyrequiredfor ioniza-

mitingfrequencyoftheseries (theheadof

onsfromthetheoryhavebeencompletely

thalargenumberof elements,withinthe

accuracy,whichunfortunatelyisnotyetall

anceandionizationpotentialsismost

etallicvapors.Inthecase ofhydrogenthe

eculescomplicatesthesituation,butif wecould

drogenweshoulddoubtlessfindthefirstr eso-

nizationpotentialtobe intheratioof 3to4,

upontheterm(— ^J=-^, andthelatter

huscorrespondingtothefirstline,and

series.

onanceandionizationpotentialsseemto

strationofthequantumassumptionthat

twithintheatom,andthat anelectroncan-

el unlessitreceiveasufficientamount

letelytoanotherlevel.

nglyusefulevenapartialstatementof

e,letus turntohiscompletetheoryof the

atom.Heassumedfirsta Rutherfordatom

usandan electronrevolvingaboutitin

petalforceistakenas thatgivenby


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forceequaltotheproductofthe two

portionaltothesquareofthe distancebe-

esofthesystemarein thisrespectidentical

posedofthe sun,andaplanetmoving

of forceacontinuous"seriesoforbits

achorbitdeterminingthevelocityintheorbit,

dpotential)ofthe system.NowBohrin-

orybyassumingthatnotall oftheseorbits

rogenAtom'(Bohr).

particularset oforbitsinwhichtheangular

nisanintegralmultiple ofh/2X(Figure10).

usis theoneinwhichthe angularmo-

esecondis oneinwhichithas twice

onformitywiththeassumedlawofforce

iin theratioof1:4:9:16,andso on

efirstorbitbeingof theorderof1cr8cm.

onewhichwehavediscussedbefore,

ghtoccurswhentheelectronfallsfrom

t,andthatthe frequencyoftheemitted

enceinenergybetweenthetwoorbits(or

nglysimpleassumption,itis possible


/ h t t p : / / w w w . h



46/169


ewholesetofspectralseries whichweas-

MerelyfromCoulomb'slawandthe

armomentumineachorbitis amultipleof

eenergyoftheatomcorrespondingtoany

n,

henucleus,ethechargeonthe electron,

nandhthePlanckconstant.

e,andifweuse Equation8we.-find

e

resemblein formtheequationbywhich

dthespectrallinesofmonatomichydrogen,

st termofEquation10shouldbe equal

nditis sowithinthenarrowlimitsof error

ionoftheseveralquantitiesconcerned.

tomwitha nuclearchargeequalto

dpossessingasingleelectron,shouldgive

theformula

ickeringseries,aswellas certainother

rmerlybeenascribedtohydrogen,butwhich

o heliumatomsfromwhichoneofthe

ected,namely,totheionHe+.This in-

mpletelyverifiedbytheproductionofthese

rehelium.

luesofRydberg'sconstantobtainedfrom

the "enhanced"heliumseriesarenot

oughthedifferenceissmall,themethodsof

orefinedthatitcanbe measuredwithsome

wasalsoreadilyexplained,sincethemass

elynegligiblewithrespecttothemass of

helium,andthereforeinsteadof assuming

eusoccupiesa fixedpositionandtheelectron

mustbe consideredasrevolvingabouttheir

whichisveryclosetothe centerofthenucleus.

heknownmassesof thehydrogenand

valuesof theconstantintheequationsfor

beenfoundpossibletocalculatethemass

racywhichapparentlyrivalsthatgiven


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47/169


attempttodescribethe manyinterest-

nementswhichhavebeenintroducedinto

mptionofellipticalas wellascircularorbits,

tsvaryingnotcontinuouslybutin steps,

ndapplicationofquantumtheory.Manyof

onsregardingspectrallinestowhichwe

eourattentionarethusbroughtinto con-,

iple.

verynotablelist ofquantitativeagree-

ntandthesimpleassumptionofBohrsome

evingthatBohr'smodelof thehydrogen

edheliumatomis somethingmorethana

andmayrepresentanultimatereality.Never-

usin makingsuchaninference.When

ousetherwas initsprime,severalmodels

heetherwereofferedwhichrepresented

uacythepropertiesofthe electromagnetic

tthe mathematicalequationsofhydro-

ticalwiththemathematicalequationsof

mechanicalpicturesoftheetherare now

hileitseemsnaturalto usethesame

hargedpartsofan atomwhichisfound

chargedbodiesat greaterdistancesfrom

oninthesuccessofthis experimentissome-

roductionofanotherassumptionwhich

mb'slawto certainspecificorbits.This

uggestionhas yetbeenmaderegarding

hequalitativelawsgoverningtheelectron

deedthecombinationofthequantumtheory

yoftheatomseemsto resultinamodel

mesenseintermediatebetweenthoseof

rapidmotionandthoseofa staticatom,

tionsshow.

assicalelectromagnetictheorythatany

demitradiantenergy,buttheelectronin

theBohrtheoryis subjecttoconstantac-

teroftheatomandyet issupposedtoemit

chemissionofenergyfromanaccelerated

e anentirelyinevitableconsequenceevenof

sreasonwemayturn ourattentiontoa

nwhichI haveattemptedtoshow(1917)

hepropertiesoftheBohratomand theprop-

havebeenassumedfora systemcontaining

entahydrogenatomaccordingtoBohr

torbit,thatis tosayinthe moststable

by AA'asmallwirewhichmaybe brought


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48/169


.Nowif theelectronintheorbit exerts

ata distance,whentheelectronisinposition

ofpositiveelectricityin thewire

ectronisat X'therewillbe aslightflow

itedistanceof thewirefromtheatom

hewirea finitealternatingcurrentwhich

y.Suchacurrentshouldgenerateheat,

posedtobeinthe stateoflowestpossible

eno sourcefromwhichtheheatcould

wemustconcludeeitherthatsuch an

btfulPointConcerningtheBohrAtom.

roducedorthat itisproducedbutmeets

ssible.Theelectronsin themetalwire

e subjecttoquantumlaws,andsincethe

cquireowingtotheirproximityto the

eryminute,itmightbe assumedthattheir

uldoccurwithoutfrictionalloss.Indeed

edthatwithaperfectcrystalat avery

potentialgradientwillbefound tobe

tronscanbesufficientlydisplacedfromtheir

veordinaryelectricalconduction.Butwith

ytemperatureswehavenoexperimental

wouldfailevenatverysmall valuesof

ordoesthisseemlikelyontheoretical

correct,wemustconcludethatanelec-

tsuponotherelectronsnoforcewhich

n theorbit.Inotherwordsit seemsas

therassumptiontothoseof Bohr,namely,

electronmayasawholeaffectthe orbit


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49/169


ouldlookforno effectswhichdependupon

fanyelectroninits orbit.Ifthisidea

simplifyattemptsto secureadequate

ulescontainingtwoormoreelectrons.

vesuccessoftheBohrmodelwaslimited

tomicnucleusaccompaniedbyoneelectron.

ycompleteandadequatemodelsofatoms

haveso farfailed.InBohr'soriginal

nganumberof electrons,theseelectrons

gedin successiveconcentricringsabout

ectronsinanyone ringbeingequallyspaced

velocity.However,thisideahasbeen

chapterweshall discussthemorerecent

estructureofsuch anatom.

nsonspectrallines,thereappearstobe

structureof theatomwhichissodirect

thodfurnishedbythestudyofmagnetism.

mentaldifficultiesinthisfieldaregreat,

ymeagredata concerningthemagneticprop-

ventheinformationwhichwenowpos-

portancetoanytheoryofatomicandmolecular

esinamagneticfieldis inmanyrespects

ectricfield.Whentwoplatesofanelectric

eoppositelychargedtheyattractoneanother,

a positivechargeattheoneend,and a

er,isplacedbetweenthe platesittends

ositiveendapproachesthenegativeplate

achesthepositiveplate.In sodoingit

betweenthetwoplatesinaccordancewith

cattraction.

weentheplates,formerlyseparated

nysubstancetheattractiondiminishes,

original attractionandtheattractionnow

ectricconstantofthesubstancein question.

umedthatthesubstancecontainsmolecules

gedatthetwoendsand arethereforecalled

tionofthesecharges,eitherthroughthe

edipole,or throughslightdisplacements

theequilibriumpositions whichthey

edtodeterminethemagnitudeofthedielec-

ichtendtoorientthemselvesstrictlyin

ouldnotbe expectedtodosocompletely,

on,andinaccordancewiththisviewit is


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tthedielectricconstantofasubstancealways

gtemperature.

dbehavesverymuchlike thedipole

queisproportionaltowhatis calledits

caseofasimplebar magnetthismagnetic

theintensityof magnetizationandthe

poles.Ifthemagnetis anelectriccircuit

ntheamountofcurrentand thedimensions

oles,separatedbyavacuum,exertupon

whichisdiminishedif asmallmagnetis

olesandis allowedtoorientitselfincon-

orque,sothatits southendapproaches

net,anditsnorthendapproachesthesouth

ypeofOrientationofaMolecularMagnetThat

m

analogouscaseoftheelectricfield,

dbetweenthetwomagneticpolesdiminish

weenthesepoles.

nalattractionbetweenthepolesand

ertheinterveningspacehas beenfilled

tion,isknownas thepermeabilityofthe

ctiveforceisthusdiminished,thesub-

magnetic,orinextremecases,ferromagnetic.

stancecontainsmolecularmagnetswhich

nthe magneticfield,butthatthethermal

eteorientation.Itisanobservedfactthat

aramagneticsubstancesalwaysdiminishes

ure.

rclassofsubstances,havingnocounter-

gue,thatincreasetheattractionbetween

hesesubstanceswhichhavepermeabilityless

agnetic.Inatypicaldiamagneticsubstance

ndentofthetemperature.

a-anddiamagnetism,everymolecule

ircuitsororbitalelectrons.Eachelectriccir-

smallmagnet,andtheseelementarycircuitsor

tobeaffectedbytemperature,norare they


/ h t t p : / / w w w . h



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52/169

Views;the

in

odistinctviewsofthe internalstructure

bothviewstheneutral atomiscomposed

positivechargeequaltoZ,theatomic

electronssituatedaboutthiscenter.

odiclaw andthechemicalbehaviorof

ctureof arelativelystaticatom.Accord-

ctronsoccupyfixedpositionswhicharear-

saboutthenucleus.Itis notimpliedthat

splacedfromthesepositionsby theaction

nintonewpositionswhenachemicalre-

anythinginthis viewreallyincompatible

electronin rapidmotion,suchastheParson

e electronasawholeisregardedas

intheatom.This theoryofthestaticatom

assumptionthattheordinarylawsofelec-

ionarevalidwithinthe atom.

istsledtoa quitedifferentviewofthe

rfordassumestheforcesbetweenthe

eatomtobethe sameasthosewhichhold

es.Theatomisregardedas asortofplane-

rceof attractionbetweenthenucleus

bythecentrifugalforcedueto theirorbital

consideredtobearrangedin successive

ssiveshells.

obequitei ncompatible,althoughitis

nginvestigatedbychemistandbyphysicist.If

gardedastakinganessentialpartin theproc-

minthemolecule,itseemedimpossible

dbythe simplelawsofforce,andtravelling

heplanetarytheory.Thepermanenceof

eninverycomplexmolecules,isoneofthe

phenomena.Isomersmaintaintheiridentity

eslightestappreciabletransformation.An

withpowerfulreagentsoftensuffersradical

moleculewhiletheremainderappearsto


G o o g l e - d

i g i t i z e d

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o o g l e


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UCTUREOFATOMS.ANDMOLECULES

rsinconceivablethatthesepermanentthough

gurationscouldresultfromthesimplelaw

omb'slaw.

vingbarriersbetweenthetwo typesof

yBohrwhenherestrictedthe applicationof

statesororbits.I haveattemptedtoshow

atit istheorbitas awholeratherthanthe

ectronwithintheorbit thatisthething

Bohrtheory.Iftheseorbitsare infixed

theymaybeusedas thebuildingstonesof

ntiallystaticcharacter.

r,inBohr'soriginaltheorysomefeatures

atiblewiththechemist'sviewofthe atom.

ismodelsofatomscontainingmorethan

medringsofelectrons,revolvingin acom-

quiteirreconcilablewiththecommonphe-

icsevidencebegantoaccumulatewhich

heory.TheX-rayspectrographsobtained

dicateacubicorsome otherregularpoly-

tronsabouttheatom,as wasshownbythe

7).Alikeconclusionwasreachedby

heir searchingphysico-mathematicalin-

onphysicalpropertiesofcrystallinesubstances.

tainingtheviewoftheorbital electron,

makethe

lewis (valence and the structure of atoms and molecules) (acs)

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