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1、1NuclearChemistryChapter19Copyright ©TheMcGraw-HillCompanies,Inc. Permissionrequiredforreproductionordisplay.2XAZMassNumberAtomicNumberElementSymbolAtomicnumber(Z)=numberofprotonsinnucleusMassnumber(A)=numberofprotons+numberofneutrons=atomicnumber(Z)+numberofneutronsAZ1p11H1orproton1n0neutron0
2、e-10b-1orelectron0e+10b+1orpositron4He24a2oraparticle11100-10+142Review3BalancingNuclearEquationsConservemassnumber(A).Thesumofprotonsplusneutronsintheproductsmustequalthesumofprotonsplusneutronsinthereactants.1n0U23592+Cs13855Rb96371n0++2235+1=138+96+2x1Conserveatomicnumber(Z)ornuclearcharge.
3、Thesumofnuclearchargesintheproductsmustequalthesumofnuclearchargesinthereactants.1n0U23592+Cs13855Rb96371n0++292+0=55+37+2x04519.1Balancethefollowingnuclearequations(thatis,identifytheproductX):(a)(b)619.1Solution(a)Themassnumberandatomicnumberare212and84,respectively,ontheleft-handsideand208a
4、nd82,respectively,ontheright-handside.Thus,Xmusthaveamassnumberof4andanatomicnumberof2,whichmeansthatitisanαparticle.ThebalancedequationisStrategyInbalancingnuclearequations,notethatthesumofatomicnumbersandthatofmassnumbersmustmatchonbothsidesoftheequation.7(b)Inthiscase,themassnumberisthesame
5、onbothsidesoftheequation,buttheatomicnumberoftheproductis1morethanthatofthereactant.Thus,Xmusthaveamassnumberof0andanatomicnumberof-1,whichmeansthatitisaβparticle.TheonlywaythischangecancomeaboutistohaveaneutronintheCsnucleustransformedintoaprotonandanelectron;thatis,(notethatthisprocessdoesno
6、talterthemassnumber).Thus,thebalancedequationis19.18CheckNotethattheequationin(a)and(b)arebalancedfornuclearparticlesbutnotforelectricalcharges.Tobalancethecharges,wewouldneedtoaddtwoelectronsontheright-handsideof(a)andexpressbariumasacation(Ba+)in(b).19.19NuclearStabilityCertainnumbersofneutr
7、onsandprotonsareextrastablenorp=2,8,20,50,82and126Likeextrastablenumbersofelectronsinnoblegases(e-=2,10,18,36,54and86)NucleiwithevennumbersofbothprotonsandneutronsaremorestablethanthosewithoddnumbersofneutronsandprotonsAllisotopesofthee
