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1、CHAPTER4:CHEMICALBONDING·Ofthemorethanonehundredelementsthatoccurinnatureorthathavebeenproducedsynthetically,onlythenoblegasesexistnaturallyassingle,uncombinedatoms.·Theatomsofallotherelementsoccurinsomecombinedform,bondedtogether.CHEMICALBONDS:electrostaticf
2、orcesthatholdatomstogetherincompounds.CHAPTER4.1:LEWISTHEORYOFBONDING·EdwardFrankland(1852)statedthateachelementhasafixedvalencethatdeterminesitsbondingcapacity.·FriedrichKekuleillustratedabondasadashbetweenbondingatomswhichwenowcallstructuraldiagrams(fig.1pg
3、.224)·ThestorystartswithRichardAbegg(1904),wherehesuggestedthatthe“stability”ofthe“inert”(noble)gaswasduetothenumberofoutermostelectrons.·Duetogainingorlosingelectrons,theionswould,inturn,beheldtogetherbyelectrostaticcharges,resultinginanionicbondwithinacryst
4、alofsalt.EG.Na+Cl®Na++Cl-®NaClSodium+Chlorine®SodiumChlorideWhydoatomsformbondsatall?Theanswertothisquestioninvolvesenergy.Innature,systemsoflowerenergytendtobefavouredoversystemsofhigherenergy.Inotherwords,lower-energysystemstendtohaveagreaterstabilitythanhi
5、gher-energysystems.Bondedatoms,therefore,tendtohavelowerenergythansingle,uncombinedatoms.USINGLEWISSTRUCTURESTOREPRESENTATOMSINCHEMICALBONDING·Chemicalbondinginvolvestheinteractionofvalenceelectrons-theelectronsthatoccupytheoutermostprincipalenergylevelofanat
6、om.·ReadoverthekeyideasoftheLewisTheoryofbonding(page224)·WriteouttheRulesforDrawingLewisStructuresonpage225.·DrawingaLewisstructureforamoleculeletsyouseeexactlyhowmanyelectronsareinvolvedineachbond,andhelpsyoutokeeptrackofthenumberofvalenceelectrons.·Therear
7、etwowaystoshowthebondingpairsofelectrons:(i)usedotsonly(ii)uselinesbetweenatoms·Dotsarereservedforrepresentingalonepair(anon-bondingpair)ofelectrons.OCOorOCO(fourlonepairs)·Recall:Chemistsclassifysubstancesaccordingtotheirbondsandtheforcesofattractionthatexis
8、tbetweentheirparticles.·Readpages226-227:LewisStructuresandQuantumMechanics·Dothefollowingquestionspage227#1–5,6,8TYPESOFCHEMICALBONDS(i)IONICBOND(ii)COVALENTBOND(iii)METALLICBONDIONICBON
