Atomic-structure---Edublogs-–-education-blogs-for-

HISTORYOFTHEATOM460BCDemocritusdevelopstheideaofatomshepoundedupmaterialsinhispestleandmortaruntilhehadreducedthemtosmallerandsmallerparticleswhichhecalledATOMA(greekforindivisible)HISTORYOFTHEATOM1808JohnDaltonsuggestedthatallmatterwasmadeupoftinyspheresthatwereabletobouncearoundwithperfectelasticityandcalledthemATOMSHISTORYOFTHEATOM1898JosephJohnThompsonfoundthatatomscouldsometimesejectafarsmallernegativeparticlewhichhecalledanELECTRONHISTORYOFTHEATOMThompsondevelopstheideathatanatomwasmadeupofelectronsscatteredunevenlywithinanelasticspheresurroundedbyasoupofpositivechargetobalancetheelectron'scharge1904likeplumssurroundedbypudding.PLUMPUDDINGMODELHISTORYOFTHEATOM1910ErnestRutherfordoversawGeigerandMarsdencarryingouthisfamousexperiment.theyfiredHeliumnucleiatapieceofgoldfoilwhichwasonlyafewatomsthick.theyfoundthatalthoughmostofthempassedthrough.About1in10,000hitHISTORYOFTHEATOMgoldfoilheliumnucleiTheyfoundthatwhilemostoftheheliumnucleipassedthroughthefoil,asmallnumberweredeflectedand,totheirsurprise,someheliumnucleibouncedstraightback.heliumnucleiHISTORYOFTHEATOMRutherford’snewevidenceallowedhimtoproposeamoredetailedmodelwithacentralnucleus.Hesuggestedthatthepositivechargewasallinacentralnucleus.WiththisholdingtheelectronsinplacebyelectricalattractionHowever,thiswasnottheendofthestory.HISTORYOFTHEATOM1913NielsBohrstudiedunderRutherfordattheVictoriaUniversityinManchester.BohrrefinedRutherford'sideabyaddingthattheelectronswereinorbits.Ratherlikeplanetsorbitingthesun.Witheachorbitonlyabletocontainasetnumberofelectrons.Bohr’sAtomelectronsinorbitsnucleusHELIUMATOM+NN+--protonelectronneutronShellWhatdotheseparticlesconsistof?ATOMICSTRUCTUREParticleprotonneutronelectronCharge+vecharge-vechargeNocharge11nilMassATOMICSTRUCTUREthenumberofprotonsinanatomthenumberofprotonsandneutronsinanatomHe24AtomicmassAtomicnumbernumberofelectrons=numberofprotonsATOMICSTRUCTUREElectronsarearrangedinEnergyLevelsorShellsaroundthenucleusofanatom.•firstshellamaximumof2electrons•secondshellamaximumof8electrons•thirdshellamaximumof8electronsATOMICSTRUCTURETherearetwowaystorepresenttheatomicstructureofanelementorcompound;1.ElectronicConfiguration2.Dot&CrossDiagramsELECTRONICCONFIGURATIONWithelectronicconfigurationelementsarerepresentednumericallybythenumberofelectronsintheirshellsandnumberofshells.Forexample;NNitrogen7142in1stshell5in2ndshellconfiguration=2,52+5=7ELECTRONICCONFIGURATIONWritetheelectronicconfigurationforthefollowingelements;CaOClSiNa2040112381716351428B115a)b)c)d)e)f)2,8,8,22,8,12,8,72,8,42,32,6DOT&CROSSDIAGRAMSWithDot&CrossdiagramselementsandcompoundsarerepresentedbyDotsorCrossestoshowelectrons,andcirclestoshowtheshells.Forexample;NitrogenNXXXXXXXN714DOT&CROSSDIAGRAMSDrawtheDot&Crossdiagramsforthefollowingelements;OCl8171635a)b)OXXXXXXXXClXXXXXXXXXXXXXXXXXXSUMMARY1.TheAtomicNumberofanatom=numberofprotonsinthenucleus.2.TheAtomicMassofanatom=numberofProtons+Neutronsinthenucleus.3.ThenumberofProtons=NumberofElectrons.4.Electronsorbitthenucleusinshells.5.Eachshellcanonlycarryasetnumberofelectrons.Isotopes•Atomsofthesameelement(sameZ)butdifferentmassnumber(A).•Boron-10(10B)has5pand5n•Boron-11(11B)has5pand6n10B11BTwoisotopesofsodium.LearningCheck–CountingNaturallyoccurringcarbonconsistsofthreeisotopes,12C,13C,and14C.Statethenumberofprotons,neutrons,andelectronsineachofthesecarbonatoms.12C13C14C666#p+_____________________#n_____________________#e-_____________________Answers12C13C14C666#p+666#no678#e-666Relativeatomicmass,Ar•Atomsareamazinglysmall.Inordertogetagramofhydrogen,youwouldneedtocountout602,204,500,000,000,000,000,000atoms(tothenearest100,000,000,000,000,000).•Itwouldbesillytomeasurethemassesofatomsinconventionalmassunitslikegrams.Instead,theirmassesarecomparedwiththemassofanatomofthecarbon-12isotope,takenasastandard.Wecallthisthe“carbon-12scale”.•Onthisscaleoneatomofthecarbon-12isotopeweighsexactly12units.•Anatomofthecommonestisotopeofmagnesiumweighstwiceasmuchasthisandisthereforesaidtohavearelativeisotopicmassof24.•Anatomofthecommonestisotopeofhydrogenweighsonlyonetwelfththatofthecarbon-12isotope,andsohasarelativeatomicmassof1.•Thebasicunitonthisscaleistherefore1/12ofthemassofa12Catom.Everythingelseismeasuredrelativetothat.•Therelativeatomicmass(RAM)ofanelement(asopposedtooneofitsisotopes)isgiventhesymbolArandisdefinedby:TheRAMistheweightedaverageofthemassesoftheisotopesrelativeto1/12ofthemassofacarbon-12atom.Whatisa“weightedaverage”?FindingtheRAMofchlorine.•Inanysampleofchlorine,someatomshavearelativemassof35;othersarelativemassof37.•Asimpleaverageof35and37is,ofcourse,36–butthisisnottherelativeatomicmassofchlorine.•Theproblemisthattherearen’tequalnumbersof35Cland37Cl.•Atypicalsampleofchlorinehas:35Cl75%37Cl25%•Ifyouhad100typicalatomsofchlorine,75wouldbe35Cland25wouldbe37Cl.•Thetotalmassofthe100atomswouldbe(75x35)+(25x37)=3550•Theaveragemassof1atomwouldbe3550/100=35.5•Theweightedaverageiscloserto35than37becausetherearemore35Clatomsthan37Clatoms.Aweightedaverageallowsfortheunequalproportions.•Wehavejustcalculatedther