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Lecture 18

CHEM 1201 Lecture Notes - Lecture 18: Valence Electron, Electron Shell, Electron ConfigurationPremium


Department
Chemistry
Course Code
CHEM 1201
Professor
Kolniak
Lecture
18

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Chem1201Lecture18Chapter8:BasicConceptsaboutChemicalBonding
● Thepropertiesofmanymaterialscanbeunderstoodintermsoftheirmicroscopic
propertiesofmoleculesthatinclude:
theconnectivitybetweenatomsand 
The3Dshapeofthemolecule. 
○ WeconsiderthreeTYPESofbondswithinmolecules(intramolecularforces):
■ IONICbond(electrostaticforceswhichholdionstogether,e.g.NaCl);
■ COVALENTbond(resultsfromsharingelectronsbetweenatoms,e.g.
Cl2);
■ METALLICbonding(referstometalnucleifloatinginaseaofelectrons,
e.g.Na(s)).
○ InALLchemicalbonds,electronsareSHAREDandTRANSFERREDbetween
atoms.
LewisSymbolsandtheOctetRule
● Allchemicalbondsareformedfromatransfer/sharingofelectronsbetweenatoms.
● TheelectronsinvolvedinbondingarecalledVALENCEelectrons.
● Valenceelectronsarefoundintheincomplete,outermostelectronshellofanatom(the
numberofvalenceelectronsavailableforbondingisrepresentedbythecolumnnumber
thatcontainsthesymbol).
● Asapictorialunderstandingofwherethevalenceelectronsareinanatom,werepresent
theelectronsasDOTSaroundthesymboloftheelement.
● ThenumberofelectronsavailableforbondingisindicatedbyUNPAIREDdots.
● ThesepictorialsarecalledLEWISsymbols.
● Wegenerallyplacetheelectronsonfoursidesofasquarearoundtheelementsymbol
● AnOCTET:
○ weknowthatns^2np^6isatypeofnoblegasconfiguration.Weassumethatan
atomisSTABLEwhensurroundedby8electrons(4electronpairs).Ex.[Ne]
ValenceElectrons
● Allelectronsintheoutermostshell(wemeann);thatisoutsidethenoblegas
configurationofanatomorion=valenceelectrons.
● Outermostshellcontainsallsubshells(ie.nandeachlvalue)withhighest"n"quantum
number
● Exception:ifdelectronsarepresent,thenthehighestdsubshellisincludedinvalence
shellbutonlyifhighestdsubshellisNOTcompletelyfilled(ie.d10configurationisfilled)
thisleadstooctetexceptionsandtheexpandedvalence,Iwillgettoalittlebitlater.
● BUT,keepinmindempty:sandporbitalsthatbelongtothesameshell(n);somehave
emptydorbitalsthatbelongtothesameshellontherowbelow.
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