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1、Chapter4ThePeriodicLaws4.1IntroductionThemostconspicuousfailureofquantumphysics,asatheoryofchemistry,isthedemonstratedinabilitytoaccountindetailfortheobservedperiodicorderoftheelements,thesinglemostimportantfeatureoftheoreticalchem-istry.Theimportanceofthisfai
2、lure,ifnotcompletelyignored,isroutinelyunderplayedinelementarychemistrytexts,bystatementssuchas[61]:′′Weneednotdwellontheseexceptionsbeyondnotingthattheyoccur.′′Asupposedlybetterinformedsource[51]states:′′....the4sstate,whichhasahigherenergythanthe3dstateinhyd
3、rogen,isdepressedbecauseofitslowangularmomentum,whichcausesitsorbitaltobelargeatsmallr,whereitcanfeelthefullnuclearattraction.′′Still,thesenon-explanations1aregenerallyconsideredsufficienttorationalizealldiscrepanciesbetweenobservedandpredictedelectronicconfigura
4、tions.Suchenthusiasmisunfortunateinscience.Itprovideslittleincentiveforfurtheranalysisonceaproblemisdeclaredsolved.Thestructureoftheperi-odictableisaproblemofthistype:asachemicalproblemitreferstosystems,conditionedbytheirenvironment,andnottoanisolatedentitysuc
5、hasahy-drogenatom.Theenergyspectrumofahydrogenelectroncantherefore,by1Notethatthenslevelsonthecoinagemetalsareconsistentlyathigherenergythanthe(n−1)dlevels.129130CHAPTER4.THEPERIODICLAWSdefinition,notaccountfortheobservedperiodictableoftheelements,whileadhocadj
6、ustmentsonlymaskthedeficiencieswithoutaddressingthefun-damentalproblem.Thisproblemisbestappreciatedonre-examinationofperiodicmaterialsystems,especiallywhenthemorerepresentativesample,consistingofallstable,non-radioactivenuclides[62]isconsidered.4.2NuclidePeriod
7、icity204060801001201401601802002202402601+τ21.0NeCaYb0.9SeHgSn0.80.7τ0.60.50.41−τNeutronImbalance0.3(N−Z)/ZorZ/N0.20.1NeCaSeSnYbHg01−τ220406080100120140160180200220240260MassNumberFigure4.1:Neutronimbalanceasafunctionofmassnumberfortheisotopesofselectedelement
8、sBeforethediscoveryofneutrons,thefamiliarempiricalformoftheperi-odictablewasestablishedasafunctionofatomicnumber,whichrepresentslessthanhalfthematterthatmakesupanatom,exceptforhydr
