Chemical-Periodicity

Chapter#8-ElectronConfigurationandChemicalPeriodicity8.1DevelopmentofthePeriodicTable8.2CharacteristicsofMany-ElectronAtoms8.3TheQuantum-MechanicalAtomandthePeriodicTable8.4TrendsinSomeKeyPeriodicAtomicProperties8.5TheConnectionBetweenAtomicStructureandChemicalReactivityThePeriodicTableoftheElementsScRbCsFrRaAcHfRfDuSgTcReFHeNeArGaGeKrXeRnAtPoInTlPrPmSmEuGdDyHoTmYbLuPaNpPuAmCmBkCfEsFmMdNoLr1700-17501750-18001800-1850Before1600FeSAsSbBiPbSnHgAuAgCuDateofDiscoveryoftheElementsCZnCoPtHBeMgSrYTiZrCrMnMoWNiNOCl1600-1700PTeLiNaKCaBaLaVNbTaCeOsRhIrPdCdBAlSiSeBrINdTbErRuThUBoHaMeThePeriodicTableoftheElementsFrHfRfSgTcReAtPmLuPaNpPuAmCmBkCfEsFmMdNoLr1700-17501750-18001800-18501850-1900Before1600FeSAsSbBiPbSnHgAuAgCuDateofDiscoveryoftheElementsCZnCoPtHBeMgSrYTiZrCrMnMoWNiNOCl1600-1700PTeLiNaKCaBaLaVNbTaCeOsRhIrPdCdBAlSiSeBrINdTbErRuThScRbCsRaAcGaGeInTlPoFHeNeArKrXeRnPrSmEuGdDyHoTmUYbBoDuHaMeThePeriodicTableoftheElementsRfDuSgAtEsFmMdNoLr1700-17501750-18001800-18501850-19001900-19501950-2000Before1600FeSAsSbBiPbSnHgAuAgCuDateofDiscoveryoftheElementsCZnCoPtHBeMgSrYTiZrCrMnMoWNiNOCl1600-1700PTeLiNaKCaBaLaVNbTaCeOsRhIrPdCdBAlSiSeBrINdTbErRuThScRbCsRaAcGaGeInTlPoFHeNeArKrXeRnPrSmEuGdDyHoTmUTcReHfFrPaPmYbLuNpPuAmCmBkCfBoHaMeThePeriodicTableoftheElements1700-17501750-18001800-18501850-19001900-19501950-2000Before1600FeSAsSbBiPbSnHgAuAgCuDateofDiscoveryoftheElementsCZnCoPtHBeMgSrYTiZrCrMnMoWNiNOCl1600-1700PTeLiNaKCaBaLaVNbTaCeOsRhIrPdCdBAlSiSeBrINdTbErRuThScRbCsRaAcGaGeInTlPoFHeNeArKrXeRnPrSmEuGdDyHoTmAtTcReHfFrPmYbLuPaUNpPuAmCmBkCfRfSg110111LrEsFmMdNoDuBoHaMeQuantumNumbers-SpecifytheOrbital1)PrincipalQuantumNumber=n2)Angularmomentumquantumnumber(l)3)MagneticQuantumNumber-mlForanatomwithmorethanoneelectron,weneedanadditionalquantumnumbertospecifytheelectronwithinanorbital.SplittinghydrogenatombeamsWhenabeamofhydrogenatomspassesthroughanon-uniform,externalmagneticfield,thebeamissplitintotwobeams.Why???Theelectroninthehydrogenatomgeneratesasmallmagneticfield.Itisasiftheelectronisaspinningcharge,whichgeneratesamagneticfield.Thedirectionofthespingeneratesamagneticmomentthatcanbeeitheralignedwithoragainstthemagneticfield.QuantumNumbers•4)SpinQuantumNumber-ms-givesthespinoftheelectron+or-•Thevaluesofthespinareeither:+1/2or-1/2•n=1l=0ml=0ms=+1/2and-1/2•n=2l=0ml=0ms=+1/2and-1/2l=1ml=-1ms=+1/2and-1/2ml=0ms=+1/2and-1/2ml=+1ms=+1/2and-1/2PauliExclusionPrinciple:Eachelectroninanatommusthaveauniquesetofquantumnumbers!Electronswiththesamespinkeepapartinspacewhereaselectronsofoppositespinmayoccupythesameregionofspace.Therefore,onlytwoelectronscanbeinthesameorbitalandthesetwoelectronsmusthaveoppositespin.AsaresultofthePauliExclusionPrinciple:¥ElectronconfigurationforH:n=1l=0ml=0ms=+1/2or-1/2¥ElectronconfigurationforHe:n=1l=0ml=0ms=+1/2n=1l=0ml=0ms=-1/2Problem:asthenumberofelectronsincrease,theorbitalenergylevelsbegintosplit.Splittingoforbitalenergylevels¥1)Theeffectofnuclearcharge:increasedattractionbetweentheelectronandnucleuslowerstheorbitalenergy.¥2)Theeffectofelectronrepulsion:additionalelectronsinthesameorbitalorininnerorbitalsshieldthenuclearcharge,whichraisestheorbitalenergy.¥3)Theeffectoforbitalshape:orbitalswithlowerlvaluespenetratefurtherandlowertheorbitalenergy.Thus,thesublevelenergiesarespdf.Becauseofthepenetration,the4sorbitalislowerenergythanfor3d.Result:1s2s2p3s3p4s3d4p5s4d5p6s4f5d6pMajorConclusionsfromStudiesofOrbitalStability1)TheEffectofNuclearCharge(Z)onOrbitalEnergyHe+&HhaveoneelectronbutHe+has2protons,thustwicetheattractiveforceontheelectrons:IonizationEnergyfortheTwo:He+=-5250kJ/moleH=-1311kJ/mole2)TheeffectofanadditionalElectrononOrbitalEnergyHehastwoelectrons,whereasHe+hasonlyone,theresultantrepulsionoftheelectronsinHeorbitalgivesahigherorbitalenergy(smallernegativenumber).EforHe+=-5250kJ/moleEforHe=-2372kJ/moleMajorConclusionsfromStudiesofOrbitalStability3)TheEffectofInnerElectronsontheEnergyofanOuterOrbital4)TheEffectofOrbitalShape(Lvalue)onOrbitalEnergyTheinnerelectrons(1s)shieldtheouterelectrons(2s)fromthefullattractiveforceofthenucleus,makingthe2sorbitalhigherinEnergy.Thisshieldingmeansthattheeffectivenuclearcharge(Zeff),thenuclearchargeanelectronactuallyexperiences,islessforanelectroninanouterorbital.EofH1s=-1311kJ/molandEofLi2s=-520kJ/molBecauseoftheirdifferentshapes,a2selectronis,ontheaverage,slightlyfurtherfromthenucleusthanthe2p,thereforewewouldexpecta2selectrontobeattractedlessstronglyandbehigherinenergy.Butbecausethe2selectronalsohasasmallprobabilityofpenetratingveryclosetothenucleus,thusloweringtheenergyofthe2selectron,makingitsenergylowerthanthe2pelectron.ElectronConfigurationofHeliumandLithium¥He1s2n=1l=0ml=0ms=+1/2n=1l=0ml=0ms=-1/2¥Li1s22s1n=1l=0ml=0ms=+1/2n=1l=0ml=0ms=-1/2n=2l=0ml=0ms=-1/2OrbitalBoxDiagramsHtoBeElementSymbolElectronOrbitalBoxDiagramsConfigurationHydrogenH1s1HeliumHe1s2LithiumLi1s22s1BerylliumBe1s22s21s1s1s1s2s2s2s2sHundsRule¥Foranatominitsground-stateconfiguration,allunpairedelectronshavethesamespinorientation.¥Thereforeelectronstendtooccupyallfreeorbitalsofthesameen