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OCRCHEMISTRYANOTESFORTOPIC1111ATOMS121ELECTRONSTRUCTURE131PERIODICITY111ATOMSAPROTONS,NEUTRONSANDELECTRONSATOMSAREMADEUPOFTHREEFUNDAMENTALPARTICLESPROTONS,NEUTRONSANDELECTRONSPROTONSANDNEUTRONSAREFOUNDINTHENUCLEUSANDARECOLLECTIVELYCALLEDNUCLEONSELECTRONSORBITTHENUCLEUSINASIMILARWAYTOTHATINWHICHPLANETSORBITASUNINBETWEENTHEELECTRONSANDNUCLEUSTHEREISNOTHINGEMPTYSPACETHENUCLEUSISVERYSMALLIFANATOMWERETHESIZEOFAFOOTBALLPITCH,THENUCLEUSWOULDBETHESIZEOFADRAWINGPINTHEBASICPROPERTIESOFTHESETHREEPARTICLESCANBESUMMARIZEDINTHEFOLLOWINGTABLEPARTICLECHARGEMASSPROTON1UNITAPPROX1UNITNEUTRONNOCHARGEAPPROX1UNITELECTRON1UNITAPPROX1/1840UNITSVERYSMALL1UNITOFCHARGEIS1602X1019COULOMBSAPROTONISGIVENACHARGEOF1ANDANELECTRONACHARGEOF1ALLCHARGESAREMEASUREDINTHESEUNITS1UNITOFMASSIS1661X1027KGTHISISALSONOTACONVENIENTNUMBER,SOWEUSE“ATOMICMASSUNITS”SINCETHEMASSOFPROTONSANDNEUTRONSVARIESSLIGHTLYDEPENDINGONTHENUCLEUS,THENINORDERTODEFINEAN“ATOMICMASSUNIT”WENEEDTOCHOOSEONENUCLEUSASASTANDARDFORTHISPURPOSE126C,OR“CARBON12”,WASCHOSENBECAUSEITSMASSPERNUCLEON1661X1027KGISAROUNDAVERAGE,WHICHMEANSALLTHEOTHERNUCLEIHAVEMASSESCLOSETOWHOLENUMBERSANATOMICMASSUNITISTHUSDEFINEDAS1/12THOFTHEMASSOFONEATOMOFCARBON12EVERYTHINGELSEISMEASUREDRELATIVETOTHISQUANTITYBATOMICNUMBERS,MASSNUMBERSANDISOTOPESANATOMISNAMEDAFTERTHENUMBEROFPROTONSINITSNUCLEUSIFTHENUCLEUSOFANATOMHAS1PROTON,ITISHYDROGENIFITHASTWOPROTONS,ITISHELIUMIFITHAS3,ITISLITHIUMETCTHENUMBEROFPROTONSINTHENUCLEUSOFANATOMISCALLEDTHEATOMICNUMBERITHASTHESYMBOLZTHEATOMICNUMBERISTHENUMBEROFPROTONSINTHENUCLEUSOFANATOMNOTALLATOMSOFTHESAMEELEMENTHAVEEQUALNUMBERSOFNEUTRONSTHISMAYVARYSLIGHTLYTHESUMOFTHENUMBEROFPROTONSANDNEUTRONSINTHENUCLEUSOFANATOMISCALLEDITSMASSNUMBERITISREPRESENTEDBYTHESYMBOLATHEMASSNUMBERISTHESUMOFTHENUMBEROFPROTONSANDNEUTRONSINTHENUCLEUSOFANATOMTHENUCLEUSOFANATOMCANTHUSBECOMPLETELYDESCRIBEDBYITSMASSNUMBERANDITSATOMICNUMBERITISGENERALLYREPRESENTEDASFOLLOWSAZEEG94BE,126C,2412MGATOMSWITHTHESAMEATOMICNUMBERBUTWITHDIFFERENTMASSNUMBERSIEDIFFERENTNUMBERSOFNEUTRONSARECALLEDISOTOPESISOTOPESAREATOMSWITHTHESAMEATOMICNUMBERBUTWITHDIFFERENTMASSNUMBERSEGMAGNESIUMATOMICNUMBER12HAS3NATURALLYOCCURRINGISOTOPES2412MG12PROTONS,12NEUTRONS2512MG12PROTONS,13NEUTRONS2612MG12PROTONS,14NEUTRONSINANEUTRALATOM,THENUMBEROFPROTONSANDELECTRONSARETHESAMEHOWEVER,MANYELEMENTSDONOTEXISTASNEUTRALATOMS,BUTEXISTASIONSIONSARESPECIESINWHICHTHEPROTONANDELECTRONNUMBERSARENOTTHESAME,ANDHENCEHAVEANOVERALLPOSITIVEORNEGATIVECHARGETHENUMBEROFELECTRONSINASPECIESCANBEDEDUCEDFROMITSCHARGEEG2412MG212P,12N,10E2412MG12P,12N,11E2412MG12P,12N,12E2412MG12P,12N,13EBRELATIVEATOMICMASSTHEMASSOFANATOMISMEASUREDINATOMICMASSUNITS,WHEREONEUNITIS12THOFTHEMASSOFONEATOMOFCARBON12THERELATIVEISOTOPICMASSOFANISOTOPEISTHERATIOOFTHEMASSOFONEATOMOFTHATISOTOPETO1/12THOFTHEMASSOFONEATOMOFCARBON12ITISUSUALLYVERYCLOSETOAWHOLENUMBERRATIOISOTOPEMASSNUMBERRELATIVEISOTOPICMASS11H1100642HE4400394BE990122713AL27269195927CO5958933THEMASSESOFPROTONSANDNEUTRONSVARYSLIGHTLYFROMISOTOPETOISOTOPE,SOTHERELATIVEISOTOPICMASSISNOTEXACTLYAWHOLENUMBERTHERELATIVEATOMICMASSOFANATOMISTHERATIOOFTHEAVERAGEMASSOFONEATOMOFTHATELEMENTTO1/12THOFTHEMASSOFONEATOMOFCARBON12THERAMISTHEAVERAGEMASSOFALLTHEISOTOPES,ANDISOFTENNOTCLOSETOAWHOLENUMBERELEMENTCOMMONMASSNUMBERSRELATIVEATOMICMASSMG24,25,262432CL35,373545BR79,817991BA134,135,136,137,13813733SPECIESCONSISTINGOFMORETHANONEATOMALSOHAVEACHARACTERISTICMASSTHERELATIVEMOLECULARMASSOFAMOLECULEISTHERATIOOFTHEAVERAGEMASSOFTHATMOLECULETO1/12THOFTHEMASSOFANATOMOFCARBON12THERELATIVEFORMULAMASSOFACOMPOUNDISTHERATIOOFTHEAVERAGEMASSOFONEFORMULAUNITOFTHATCOMPONDTO1/12THOFTHEMASSOFANATOMOFCARBON12THERELATIVEMOLECULAR/FORMULAMASSOFASPECIESISTHESUMOFTHERELATIVEATOMICMASSESOFITSCONSTITUENTATOMSEGTHERELATIVEMOLECULARMASSOFCO2IS120160160440THERELATIVEATOMICMASSCANBECALCULATEDBYTHEFORMULAPERENTAGEABUNDANCEOFEACHISOTOPEXMASSOFEACHISOTOPE100EGNEONCONSISTSOF90NEON20AND10NEON22WHATISITSRELATIVEATOMICMASSRAM90X2010X22/100202121ELECTRONSTRUCTUREAENERGYLEVELSELECTRONSDONOTORBITTHENUCLEUSRANDOMLYTHEYOCCUPYCERTAINFIXEDENERGYLEVELSEACHATOMHASITSOWNUNIQUESETOFENERGYLEVELS,WHICHAREDIFFICULTTOCALCULATEBUTWHICHDEPENDONTHENUMBEROFPROTONSANDELECTRONSINTHEATOMENERGYLEVELSINANATOMCANBENUMBERED1,2,3,TOINFINITY1ISTHELOWESTENERGYLEVELCLOSESTTOTHENUCLEUSANDENERGYLEVELINFINITYCORRESPONDSTOTHEENERGYOFANELECTRONWHICHISNOTATTRACTEDTOTHENUCLEUSATALLTHEENERGYLEVELSTHUSCONVERGEASTHEYAPPROACHINFINITYN1N2N3N4N6N5BORBITALSANDSUBLEVELSELECTRONSDONOTINFACTORBITTHENUCLEUSINANORDERLYWAYINFACTTHEYOCCUPYAREASOFSPACEKNOWNASORBITALSTHEEXACTPOSITIONOFANELECTRONWITHINANORBITALISIMPOSSIBLETOIMAGINEANORBITALISSIMPLYANAREAOFSPACEINWHICHTHEREISAHIGHPROBABILITYOFFINDINGANELECTRONORBITALSCANHAVEANUMBEROFDIFFERENTSHAPES,THEMOSTCOMMONOFWHICHAREASFOLLOWSSORBITALSTHESEARESPHERICALEVERYENERGYLEVELCONTAINSONESORBITALANSORBITALINTHEFIRSTENERGYLEVELISA1SORBITALANSORBITALINTHESECONDENERGYLEVELISA2SORBITAL,ETCPORBITALSTHESEARESHAPEDLIKEA3DFIGUREOFEIGHTTHEYEXISTINGROUPSOFTHREEEVERYENERGYLEVELEXCEPTTHEFIRSTLEVELCONTAINSTHREEPORB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