大学化学课件-国外原版教材.ppt

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1、Atoms,Molecules,andIonsChapter2DavidP.WhiteUniversityofNorthCarolina,WilmingtonCopyright1999,PRENTICEHALL1Chapter2JohnDalton:EachelementiscomposedofatomsAllatomsofanelementareidentical.Inchemicalreactions,theatomsarenotchanged.Compoundsareformedwhenatomsofmorethanoneelementcombine.Dalton’slawofm

2、ultipleproportions:Whentwoelementsformdifferentcompounds,themassratiooftheelementsinonecompoundisrelatedtothemassratiointheotherbyasmallwholenumber.TheAtomicTheoryofMatterCopyright1999,PRENTICEHALL2Chapter2TheancientGreekswerethefirsttopostulatethatmatterconsistsofindivisibleconstituents.Latersc

3、ientistsrealizedthattheatomconsistedofchargedentities.CathodeRaysandElectronsAcathoderaytube(CRT)isahollowvesselwithanelectrodeateitherend.Ahighvoltageisappliedacrosstheelectrodes.TheDiscoveryofAtomicStructureCopyright1999,PRENTICEHALL3Chapter2CathodeRaysandElectronsThevoltagecausesnegativeparti

4、clestomovefromthenegativeelectrodetothepositiveelectrode.Thepathoftheelectronscanbealteredbythepresenceofamagneticfield.TheDiscoveryofAtomicStructureCopyright1999,PRENTICEHALL4Chapter2CathodeRaysandElectronsConsidercathoderaysleavingthepositiveelectrodethroughasmallhole.Iftheyinteractwithamagnet

5、icfieldperpendiculartoanappliedelectricfield,thecathoderayscanbedeflectedbydifferentamounts.Theamountofdeflectionofthecathoderaysdependsontheappliedmagneticandelectricfields.Inturn,theamountofdeflectionalsodependsonthechargetomassratiooftheelectron.TheDiscoveryofAtomicStructureCopyright1999,PREN

6、TICEHALL5Chapter2CathodeRaysandElectronsTheDiscoveryofAtomicStructureCopyright1999,PRENTICEHALL6Chapter2CathodeRaysandElectronsIn1897,Thomsondeterminedthechargetomassratioofanelectrontobe1.76108C/g.Goal:findthechargeontheelectrontodetermineitsmass.TheDiscoveryofAtomicStructureCopyright1999,PREN

7、TICEHALL7Chapter2CathodeRaysandElectronsConsiderthefollowingexperiment:Oildropsaresprayedaboveapositivelychargedplatecontainingasmallhole.Astheoildropsfallthroughthehole,theyaregivenanegativecharge.Gravityforcesthedropsdownw