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1、第八章Themostpopularformoftheperiodictableisthelongformthatisfoundinsidethebackcoverofthisbook.Theperiodsconsistofthoseelementsthatarearrangedinhorizontalrowsinthetable.Theorganizationissuchthatelementsofsimilarchemicalandphysicalproperties(calledgroupsorfamilies)appearinverticalcolumns.In
2、thistable,thesetofelementsappearingatthebottomandcalledthelanthanidesshouldactuallyappearinthebodyofthechartinproperorderbyatomicnumbersothatthesixthperiodhasitsrequisite32elements.Forconvenienceinreproductionthisisnotdone;but,properly,thechartshouldbeverticallycut,thesectionsseparated,
3、andthelanthanidesinsertedintheirproperpositions.Fortheactinides,whichappearbelowthelanthanidesatthebottomoftheperiodictable,thesameconsiderationspertain;theyshouldbeinsertedintheseventhChapter8PeriodicLawandElectronicStructuresl39period(asyetincomplete).Thefirstperiodconsistsofonlytwoel
4、ements,hydrogenandhelium.Subsequentperiodshave8,8,18,18,and32elements.Withtheexceptionofthefirstperiod,eachcompleteperiodbeginswithanalkalimetal(groupⅠA)—ahighlyreactive,light,silverymetal—andendswithanoblegas(group0)—anunreactive,colorlessgas.Theelementbeforethenoblegasofeachcompletepe
5、riod(again,exceptingthefirstperiod)isahalogen(groupⅦA)—averyreactivenonmetal.Thereisageneralpatternforeachoftheperiodsafterthefirst.Startingwithanalkalimetal,thepropertieschangefromelementtoelement—themetallicpropertiesfadingandbeinggraduallyreplacedbynonmetalliccharacteristics.Afterahi
6、ghlyreactivenonmetal,ahalogen,isreached,eachcompleteperiodendswithanoblegas.Sincetheperiodictableclassifiesatomsbychemicalbehavior,andsincechemicalbehaviorisdeterminedbyelectronicconfiguration,theperiodictablemayalsobesaidtoclassifyatomsbyelectronicconfiguration.Themaximumnumberofelectr
7、onsthateachenergylevelmayholdisgivenby2n2,wherenistheprincipalquantumnumberoftheshellinquestion.Henceforthen=1shell,themaximumnumberis2(1)2or2;forthen=2level,thisnumberis2(2)2or8;thesemaximumelectronpopulationsforthefirstfiveshellsaregivenintable8.1.Table8.1MaximumNumberofElect
