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1、AtomicStructureNotesAdaptedfromtheScienceHelponLine(E.Muniz/G.Maynes)I.DevelopmentoftheAtomicTheory•DemocritusmaynothavebeenthefirstoftheancientGreekstosuggestanatomictheory,thisdistinctiongoestohisteacherLeucippus,buthisnameisoftenassociatedwiththefirstatomictheory,becauseofhis
2、supportofit.ToDemocritus,atomswerecompletelysolid,homogeneous,indestructibleobjects.•JohnDalton,anEnglishchemist,mightbecalled"thefatherofthemodernatomictheory.".Duringtheearly1800’s,Dalton’sinterestsinMeteorologyandgasesledhimtoreadtheworksofAntoineLavoisierandJosephProust.Lavo
3、isierhadstatedthelawofconservationofmass:thatthemassofmaterialsbeforeachemicalreactiontakesplaceisexactlyequaltothemassofthematerialsafterthereactioniscompleted.Prousthadobservedthelawofdefiniteproportions,statingthattheproportionbymassoftheelementsinagivencompoundisalwaysthesam
4、e.Daltonfeltthatthefindingsofthesemengavestrongsupporttotheideaofatoms.HeformulatedanatomictheorythatwouldincludetheobservationsmadebyLavoisierandProust.Dalton’sAtomicTheory1)Allelementsarecomposedofatoms,whichareindivisibleandindestructibleparticles.2)Allatomsofthesameelementar
5、eexactlyalike;inparticular,theyallhavethesamemass.3)Allatomsofdifferentelementsaredifferent;inparticular,theyhavedifferentmasses.4)Compoundsareformedbythejoiningofatomsoftwoormoreelements.Inanycompound,theatomsofthedifferentelementsinthecompoundarejoinedinadefinitewhole-numberra
6、tio,suchas1to1,2to1,3to2,etc.•JosephJohnThomsonsubjectedcathoderaystomagneticandelectricfieldsandshowedthatthebeamwasdeflectedaswouldbeexpectedfornegativelychargedparticles.Hecalculatedtheratiooftheelectron’schargetoitsmass.OnApril30,1897,Thomsonannouncedthatthecathoderaysconsis
7、tedofnegativelychargedparticles,whichrepresentedfundamentalparticlesofmatter.Hewasnotthefirstpersontosuggestthattheseparticlesexisted,nordidhecointheterm"electron".Yetheisgenerallycreditedwiththediscoveryoftheelectron.HewasawardedwiththeNobelPrizeinPhysicsin1906.•J.J.Thomsonisal
8、sorememberedforhis"plum-pudding"modeloftheatom,
