Chapter3AtomicStructure

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TheHistoryoftheDevelopmentoftheHumanUnderstandingoftheAtom.akaHistoryofAtomicTheory

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Bohr The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

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Democritus460-370BC• DemocrituswasaGreekPhilosopher.

• Hebelievedthatma2erwasmadeof5nydiscretepar5clesthathecalled“atomos”(atoms).

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Diditmakesense?

•  Democritus’ideaswerehardforpeopletobelieve.•  Itseemedmuchmoreintui5vetothinkthatma2erwascon5nuous.

•  AlongcameAristotlewhowasfarmorepopular,rich,outspoken,handsomeanditwashisideasthatendured. 4

Alchemyfor2000years

• Aristotlebelievedthatanysubstancecouldbetransmuted(transformed)intoanyothersubstancesimplybychangingtherela5vepropor5onsofthe4basicquali5es.

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Alchemyfor2000years•  Theideaoftransmuta6onlaidthefounda5onforalchemy

•  Alchemistsweresearchingfortheevolu5onfromignorancetoenlightenment.Theyweresearchingforthe

•  elixiroflife•  philosopher’sstone

•  Thisleadtothesearchfortheabilitytransmutema2er.

•  Intheirunsuccessfulsearch,tochangeleadintogold,theydidalotofgoodexperimenta5onthatlaidthefounda5onformodernscience. 6

TheImportanceofthePrintingPress

• Theinven5onoftheprin5ngpressinthe1400’sallowedinforma5ontobeeasilyrecordedandideascouldbemoreeasilyexchanged.

• EvidenceagainstAristotle’smodelofma2erbegantoaccumulate. 7

RobertBoyle1627-1691• ReferredtoastheFatherofModernChemistry

• Hewasoneofthefirsttopublishalltheexperimentaldetailsofhiswork,includingexperimentsthatdidnotwork.

• BoylerevivedDemocritus’ideasbyproposingthatasubstancewasnotelementifitwasmadeoftwoormorecomponents.

• Although,hisworkprimarilystudiedtheinverserela5onshipbetweenthepressureandvolumeofgases.

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Marie-AnneandAntoineLavoisier1743-1794

• Referredtoasthemotherandfatherofmodernchemistry

•  Theystudiedvarioustypesofreac5onsinvolving:

~oxygen-respira5on~burningandrus5ng~metricsystem~lawofconserva.onofmass

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Gas generating apparatus.

Lavoisier•  TheLawofConserva5onofmassstatesthatma2ercan'tbecreatedordestroyed.

•  Itcanonlybetransformed!

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AntoineLavoisierThemanywaysyoucouldstate:

TheLawofConservationofMass• Thereisnodetectablechangeinthetotalmassofmaterialswhentheyreactchemicallytoformnewmaterials.

• Themassoftheproductswillequalthemassofthereactantsinachemicalreac5on.

• Duringachemicalreac5on,ma2erisneithercreatednordestroyed.

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JosephGay-Lussac(1778-1850)• Gay-Lussacwasaballoonist.

• Becauseofhishobby,hewasveryinterestedingases.

• Hedeterminedthatthegassescombineindefinitera6osbyvolume.

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JosephProust(1754-1826)• By1790Proustrecognizedthathydrogenandoxygencombinedindefinitera6osbymass.

•  LawofConstantComposi5on

•  Ifmoregaswereavailablethantheidealra5opredicts,thatgaswouldbele]overa]erthereac5on.

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Proust&Gay-LussacTheLawofConstantComposition• Elementscombineindefinitemassra5ostoformcompounds.

• Agivenchemicalcompoundalwayscontainsthesamepropor5onbymassofitscons5tuentelements.

• Therela5veamountofeachelementinapar5cularcompoundisalwaysthesame,regardlessofprepara5onorsource. 14

JohnDalton(1766-1844)• DaltonusedtheworkofLavoisier,Proust,andGay-LussactoreviveDemocritus’ideathatma2erwasmadeofatoms.

• Hebasedmuchofhistheoryon

•  ThelawofConserva5onofMass

•  TheLawofConstantComposi5on

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JohnDalton(1766-1844)• Hedevelopedasystemofsymbolsforeachknownelement.

• Hissymbolswereroundtomodelthe5nyroundatomshewastheorizingabout

• Todaywehavechangedtothele2eringsystem.

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Dalton’sAtomicTheoryascomparedwithModernAtomicTheory

1.  Eachelementmadeofindivisible,minutepar5clescalledatoms.•  (Hedidn’tknowaboutprotons,neutronsorelectrons.)

2.  Allatomsofagivenelementareiden6cal.•  (Notexactly,wewilllearnaboutisotopesofthesameelementhavedifferent

mass.)

3.  Atomsofdifferentelementsaredifferentmass.•  (Isotopesofdifferentelementsmayhavethesamemass.)

4.  Atomschemicallycombineindefinitera5ostoformcompounds.

5.  Atomscanbeneithercreatednordestroyedinchemicalreac5ons.•  (Theycanbecreatedanddestroyedinanuclearreac5on,butnotinachemicalreac5on.)

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Dalton

BenFranklin(1706-1790)• BeforeDalton’sAtomicTheory,scien5stswerestudyingabouttheelectricalnatureofma2er.

• Franklinrealizedthatlighteningistheflowofelectricalenergy.

• Hecoinedthetermsposi5veandnega5veforoppositecharges.

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J.J.Thomson(1856-1940)• CathodeRayTubes•  Electricitywasappliedtocathoderaytubes.

•  Thebeamitselfcannotbeseen.Thegreenbeamiscausedbytheelectronseffectonthephosphorscreen

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“DiscoveryoftheElectron“(andProton)•  Vacuumtube.Thecathoderaytubecausedpar.clestotravelfromanelectrodeatoneendtoanelectrodeattheotherend.(calledthecathodeandanode)

•  Thebeamofpar.clescanbebentbyamagne.cforce-repelledbythenega.veendofamagnetandbehavedthesameregardlessofwhichgaswasintube.

•  Thomsonnamedthesenega.velychargedpar.cles,electrons.

•  Scien5stsknewthatma>erwasneutral,theyquickly“discovered”theprotonaswell.

•  ‘ChocolateChipCookie’model

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electrodes

magnet

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ErnestRutherford(1871-1937)• GoldFoilExperiment• Rutherfordsentfast-moving,heavy,posi.vely-chargedalphapar.clesatverythingoldfoil.

•  Thescien5stsexpectedtheywouldblastthrough.

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ErnestRutherford(1871-1937)•  Theywereamazedthatsomeweredeflected(1in8000)

•  Rutherfordsuggestedthatthedeflectedpar.cleshitaverysmalldenseposi.velychargedmass-thenucleus!

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wow Oooh whoa

Yikes amazing

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HowtheViewoftheAtomwasRevised• Daltonthoughtthatatomsweresolidindivisiblepar5cles(yr1810)

•  Thomsonrevisedtheviewtothe“chocolatechipcookie”model(yr1890)

• Rutherfordrevisedtheviewtoincludetheverysmalldensenucleuswithelectronsoutsidethenucleus,perhapsinrings(yr1910)

• Bohrprovidedexperimentalevidencetosupportthatelectronsresidedinenergylevelsassociatedwithrings(yr1915) 23

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Bohr

Theend

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Bohr In later chapter

What’sInsidetheAtom?

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• Protons ~ Positively charged particles

• Neutrons ~ Neutral particles

• Electrons ~ Negatively charged particles

What’swrongwiththisdiagram?•  Itshowsthenucleus(protonsandneutronstobehugeandthisisNOTtrue.

•  ThenucleusisverySMALLSIZE,buthasveryLARGEMASS.

• Whiletheelectronsaresmallthemselves,theytakeupLOTSofSPACEandhaveveryLITTLEMASS.

•  Subatomicpar5cles-protons,neutrons,andelectronsareSOOOooooosmallthatmostscien5stsdon’teverreallyworryabouttheirsize,butprotonsandneutronsareabout1/3thesizeofanelectron.

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ThisisBetter…• Thisdiagramisabitbe2er…• Butthesizerela5onshipdemonstratedbelowisevenbe2er.

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nucleus .

growevenlarger…•  Theclassroomanalogy:• Placea5nyatominthecenterofourclassroomandexpandtheatom−nucleusandelectroncloud−propor5onately.

• Whentheelectroncloud(theatom)growstobethesizeoftheroom,thenucleuswouldbe1mminthecenteroftheroom.

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nucleus .

andstilllarger…• con5nuetopropor5onatelyexpandthisatombeyondthesizeofourclassroom,

• whentheelectroncloud(theatom)growstobethesizeofFenwayPark,

• thenucleuswouldbeamarbleinthecenteroftheroom

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nucleus .

WhatabouttheMassoftheseParticles?•  YoucertainlydoNOTneedtoknowthetablebelow.

• Butyoushouldrealizethatwhileallthreepar5clesareunbelievablylightweight…

• ProtonsandneutronsareVERYheavycomparedtotheelectrons-approximately20005mesheavier.

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InSummary:SizevsMass•  TheprotonsandneutronsinsidethenucleusareverysmallinsizethemselvesandtakeupVERYLITTLESPACEasagroup,buttheyareVERYHEAVY.

•  TheelectronsoutsidethenucleusareVERYLIGHTWEIGHT,andwhiletheyareverysmallpar5clesindividually,togethertheytakeupMOSTOFTHESPACEwithintheatom.

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NavigatingthePeriodicTable

Whatdothenumbersmean?• Atomicnumber

• numberofprotons=numberofelectronsforanatom

• Atomicmass•  averagemassofalltheisotopes

• Massnumber• Atomicmassroundedtothenearestwholenumber

•  sumofprotons+neutrons33 Li

3 6.941

Li

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InformationinthePeriodicTable•  Allelementsareiden5fiedbytheiratomicnumber.•  Foranatom,atomicnumbertellsusthe#ofprotons=#ofelectrons.

•  Theothernumberistheaverageatomicmass.•  averagemassofalltheisotopes•  Itistheaveragemassingramsofaverylargebunchofatoms,amoleofatoms.

• Whenroundedtothenearestwholenumberatomicmassbecomesthemassnumber.

•  Themass#=protons+neutrons.•  Thusmass#-atomic#=neutrons.

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Li Lithium

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6.941

Li 7 - 3

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ProtonsNeutronsElectrons• Whatdoestheperiodictabletellus?

Determinethenumberofprotons,neutrons,andelectronsinanatomofVanadium.23V23p,28n,23e•  AtomicnumberofV=23•  Sothenumberofprotons=23•  Sincethesymbolrepresentsanatom,andatomsare

neutral,theprotons=electrons•  Thusthenumberofelectrons=23•  Forthemostcommonisotope,usetheaveragemass=

50.94androundtothenearestwholenumberforthemassnumber=51

•  Thusthenumberofneutronsis51-23=2836

Determinethenumberofprotons,electrons,andneutronsinanatomofArgon.18Ar(atomicmass=39.948)protons,neutrons,electrons.

18p,22n,18e

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Determinethenumberofprotons,electrons,andneutronsinthefollowingatomsprotons,neutrons,electrons

1. Iron(Fe)2. Potassium(K)3. 15P4. Silver5. 56Ba

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1.  26p, 26e, 30n 2.  19p, 19e, 20n 3.  15p, 15e, 16n 4.  47p, 47e, 61n 5.  56p, 56e, 81n

Determinethenumberofprotons,electrons,andneutronsinanatomofMagnesium.12Mg(atomicmass=24.31)protons,neutrons,electrons.

12p,12n,12e

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Symbolizingatoms

• No5cewheretheatomicnumberis…

12Mg 27Co 16S(Magnesium)(Cobalt)(Sulfur)

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Whatelementisrepresentedby

4?• Xenon• Helium• Beryllium• cannotbedeterminedwithoutmoreinfo.

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Whatelementisrepresentedby

4Be• Xenon• Helium• Beryllium-4istheatomicnumberwhichiden5fiesanelement.

• cannotbedeterminedwithoutmoreinfo.

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Isotopes•  Atomic Siblings •  ElementwithSameNumberofProtons/

Electrons•  DifferentNumberofNeutrons(same

elementbutchangesweight)•  UnderstandingWeightedAverages

1.InMrLee’sclass,allofthestudentsendedupwithonlythreedifferenttestgrades:90,80,or70asshowninthechartbelow.Determinetheweightedclassaverage.•  90•  85•  80•  75•  70

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grade % of students receiving grade

90 10% 80 30% 70 60%

Weighted Average = (w1 * x1) + (w2 * x2) + ….. w = relative weight (%) (keep number as decimal i.e 60% = 0.60) x = value

1.InMrLee’sclass,allofthestudentsendedupwithonlythreedifferenttestgrades:90,80,or70asshowninthechartbelow.Determinetheweightedclassaverage.•  90•  85•  80•  75•  70

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grade % of students receiving grade

90 10% 80 30% 70 60%

[(90 × 0.1) + (80 × 0.3) + (70 × 0.6)] = 75

2.Considersomeone’sgradesinthisclass.Tests&Projectsweighted65%andquizzesandLABworkweighted35%.Howtocalculatethegrade?

1.  Averagethescoresofeachcategory

2.  weighttheaverageofeachcategorybasedonpercent

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[(77.3× 0.65) + (67.3× 0.35) = 73.8

Test & Proj

Quiz & LAB

92 58 62 73 78 85

92 86 0

68 76

Average 77.3 67.3

WhyisitanAverageAtomicMass?• Allatomsofapar5cularelementhavethesame#ofprotonsandelectrons.

• However,thenumberofneutronscanvaryfromatomtoatomofapar5cularelement.

• Atomsofthesameelement(samenumberofprotons)withdifferentnumberofneutronsarecalledisotopes.

•  Sinceneutronscreatemuchofthemassoftheatom,theseisotopeshavedifferentmasses.

•  ThemassesoftheisotopesofanelementareaveragedtogivetheAverageAtomicMass.

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It’saWeightedAverage•  TherearetwoisotopesofChlorine•  35Cland37Cl(35Clwith18nand37Clwith20n)•  You’dthinktheaveragewouldbe36,butitisnot!

•  Thisisbecauseinnaturethereis75%35Clandonly25%37Clandtheweightedaveragereflectstheseamountsthusendingupclosertothemoreabundantisotope.

• Dothemath:•  (35×0.75)+(37×0.25)=35.5

•  26.25+9.25=35.5(LookthisuponPeriodicTable)48

Symbolizingatoms

• No5cewherethemassnumberis…

35Cl&37Cl 3He&4He12C&13C (Chlorine)(Helium)(Carbon)Canalsobeshownas…Chlorine-35Chlorine-37

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3.Determinetheaverageatomicmassforarecentlydiscoveredelement,Valentium,Va.Itsisotopesarefoundinnatureaccordingtothechartbelow.Calculatetheaverageatomicmass.•  Reportyouranswertothenearest

10thsplace.

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isotope % abundance 300Va 65% 303Va 30% 304Va 5%

3.Determinetheaverageatomicmassforarecentlydiscoveredelement,Valentium,Va.Itsisotopesarefoundinnatureaccordingtothechartbelow.Calculatetheaverageatomicmass.•  Reportyouranswertothenearest10thsplace.

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isotope % abundance 300Va 65% 303Va 30% 304Va 5%

[(300 × 0.65) + (303× 0.3) + (304 × 0.05)] = 301.1

4.CalculatingPercentAbundance•  IfyouknewthereareonlytwoisotopesofChlorine•  35Cland37Cl•  ThePeriodicTabletellsyouaverageatomicmassis35.5•  Youcancalculatethe%abundance•  Labeloneofthefrac5onas(x),theotheras(1−x)•  Thensolveforx37x+35(1−x)=35.537x+35−35x=35.52x+35-35=35.5–352x/2=0.5/2x=0.25

*thensolveforx=0.25,thus25%ofchlorineis37Cland75%ofchlorineis35Cl

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5.InPiela’sAPChemclass,allofthestudentsendedupwithonlytwodifferenttestgrades:90and70asshowninthechartbelow.Theaverageis74.

•  Reportthe%(tonearestwhole#)thatscored90

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grade % of students receiving grade

90 ? 70

5.InPiela’sAPChemclass,allofthestudentsendedupwithonlytwodifferenttestgrades:90and70asshowninthechartbelow.Theaverageis74.

1.Defineeithergrade90as(x)ORgrade70as(x)anddefinetheotheras(1-x)

•  thus20%oftheclassscored90,80%oftheclassscored70 54

grade % of students receiving grade

90 ? 70

90x + 70(1− x) = 7490x + 70 − 70x = 7420x = 4 x = 0.2

90(1− x) + 70x = 7490 − 90x + 70x = 74

−20x = −16 x = 0.80

6.Youwouldliketocalculatethe%abundancefoundinnatureofthenewlydiscoveredelementMaxogen,Mx.Thereareonlytwonaturallyoccurringisotopes:324Mxand327Mx.Theaverageatomicmassis325.2•  Reportthe%tothenearest10thsplaceforthe

isotopethatoccursinhighestquan5ty.

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6.Youwouldliketocalculatethe%abundancefoundinnatureofthenewlydiscoveredelementMaxogen,Mx.Thereareonlytwonaturallyoccurringisotopes:324Mxand327Mx.Theaverageatomicmassis325.2•  Reportthe%tothenearest10thsplaceforthe

isotopethatoccursinhighestquan5ty.

•  60%isthe324Mx 56

324x + 327(1− x) = 325.2324x + 327 − 327x = 325.2−3x = −1.8 x = 0.6

ProtonsNeutronsElectronsforatoms,ions,&isotopes• Keepingtrackofallthesymbolsandallthenumbers.

Whatisanion?•  anatomwhichhasgainedorlostoneormoreofitselectrons,givingitanetposi5veornega5veelectricalcharge.

•  Atomsusuallyhavethesamenumberofprotons(+)andelectrons(-)sousuallytheatomisneutral(ornocharge)

•  Remember,electronshaveanega5ve(-)chargeso…•  ~ifyoulose1electrontheatomhasanoverallposi5ve1charge•  ~ifyougain1electrontheatomhasanoverallnega5vecharge

•  Example:17Cl(Chlorine)usuallyhas17protonsand17electrons•  Ifitgains1electron,whatistheoverallcharge?

• Cl-1orCl- 58

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Determinethenumberofprotons,electrons,andneutronsinN3-7p,7n,10e•  AtomicnumberofN=7

•  Thusprotons=7•  N-3

massnumber=14•  Thusneutronsis14-7=7•  N-3

-3indicatesanionwhichisanatomthathasgained3 electrons!

•  Thuselectronsis7+3=10 59

Determinethenumberofprotons,neutrons,andelectronsin63Zn+230p,33n,28e•  AtomicnumberofZn=30

•  Thusprotons=30

•  63Zn+2Isotopemassnumber=63•  Thusneutronsis63-30=33

•  63Zn+2+2indicatesaca5onwhichisanatomthathaslost2 electrons

•  Thuselectronsis30-2=28 60

Determinethenumberofprotons,electrons,andneutronsin17O-2

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•  protons, neutrons, electrons.

8p, 9n, 10e

Symbolizingatoms

• No5cewheretheionnumberis…Cl-1 (Chlorine)Anion–nega5velychargedion

Mg2+

(Magnesium)Ca5on–posi5velychargedion

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PennyLABPenniesasIsotopes

• PRE-1982penniesweigh3.10g(95%copper)• POST-1982penniesweigh2.51g(97%zinc)