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1、PhysicsProfessionalEnglish物理学专业英语PhysicsProfessionalEnglishA3AtomsandmoleculesinmotionNEWWORDSPage.10NEWWORDSPage.11AtomsAllmatteismadefromatoms.Itwouldtakemorethanamillionmillionatomstocoverthisfullstop.Anatomhasatinycentralnucleusmadeofprotonsandneutrons(apartfromth
2、esimplestatom,hydrogen,whosenucleusisasingleproton).Orbitingthenucleusaremuchlighterparticlescalledelectrons.A3AtomsandmoleculesinmotionAnatomhasthesamenumberofelectronsasprotons,sotheamountsofnegativeandpositivechargebalance.Unlikecharges(-and+)attracteachother.Thise
3、lectricforceholdselectronsinorbitaroundthenucleus.However,theparticlesinthenucleusareheldtogetherbyastrongnuclearforce,whichisstrongenoughtoovercometherepulsionbetweentheprotons.Atomscansticktogether,insolidsforexample.Theforcesthatbindthemareattractionsbetweenopposit
4、echarges.A3AtomsandmoleculesinmotionMovingelectronsInmetals,someoftheelectronsareonlylooselyheldtotheiratoms.Thesefreeelectronscandriftbetweentheatoms.Theelectriccurrentinawireisaflowoffreeelectrons.Ifanatomgainsorloseselectrons,itisleftwithanoverall-or+charge.Charged
5、atomsarecalledions.A3AtomsandmoleculesinmotionElementsandisotopesEverythingismadefromabout100substancescalledelements.Eachelementhasadifferentnumberofprotons(andthereforeelectrons)initsatoms.Elementsexistindifferentversions,calledisotopes,eachwithadifferentnumberofneu
6、tronsinitsatoms.Examplesareshownbelow(italicnumbersareforrarerisotopes).A3AtomsandmoleculesinmotionThetotalofprotonsplusneutronsinanatomiscalledthenucleonnumber.Itisusedwhennamingdifferentisotopes,forexample:carbon-12,carbon-13,carbon-14RadioactiveisotopesThesehaveato
7、mswithunstablenuclei.Thenucleibreakup,emittingnuclearradiation.Thethreemaintypesofnuclearradiationarealphaparticles,betaparticlesandgammawaves(seeA6).A3AtomsandmoleculesinmotionSolids,liquidsandgasesAccordingtothekinetictheory,matterismadeupoftiny,randomlymovingpartic
8、les.Eachparticlemaybeasingleatom,agroupofatomscalledamolecule,oranion.Thethreenormalphasesofmatteraresolid,liquid,andgas.Sol