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Chapter2
Atoms,Molecules,
andIons
AtomicTheoryofMatter Thetheorythatatomsarethefundamentalbuildingblocksofmatterreemergedintheearly19thcentury,championedbyJohnDalton.
Dalton’sPostulates Eachelementiscomposedofextremelysmallparticlescalledatoms.
Dalton’sPostulates Allatomsofagivenelementareidenticaltooneanotherinmassandotherproperties,buttheatomsofoneelementaredifferentfromtheatomsofallotherelements.
Dalton’sPostulates Atomsofanelementarenotchangedintoatomsofadifferentelementbychemicalreactions;atomsareneithercreatednordestroyedinchemicalreactions.
Dalton’sPostulates Compoundsareformedwhenatomsofmorethanoneelementcombine;agivencompoundalwayshasthesamerelativenumberandkindofatoms.
LawofConstantComposition
JosephProust(1754–1826)Alsoknownasthelawofdefiniteproportions.Theelementalcompositionofapuresubstancenevervaries.
MultipleProportions
MultipleProportions
LawofConservationofMass Thetotalmassofsubstancespresentattheendofachemicalprocessisthesameasthemassofsubstancespresentbeforetheprocesstookplace.
TheElectronStreamsofnegativelychargedparticleswerefoundtoemanatefromcathodetubes.J.J.Thompsoniscreditedwiththeirdiscovery(1897).
TheElectron Thompsonmeasuredthecharge/massratiooftheelectrontobe1.76?108coulombs/g.
MillikanOilDropExperiment Oncethecharge/massratiooftheelectronwasknown,determinationofeitherthechargeorthemassofanelectronwouldyieldtheother.
MillikanOilDropExperiment RobertMillikan(UniversityofChicago)determinedthechargeontheelectronin1909.
Radioactivity:Thespontaneousemissionofradiationbyanatom.FirstobservedbyHenriBecquerel.AlsostudiedbyMarieandPierreCurie.
RadioactivityThreetypesofradiationwerediscoveredbyErnestRutherford:?particles?particles?rays
TheAtom,circa1900:“Plumpudding”model,put
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