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第頁共頁高二物理教案：共價鍵與固體導(dǎo)電性Covalentbondsareatypeofchemicalbondthatoccurswhentwoatomsshareapairofelectrons.Covalentbondscanformbetweentwonon-metalatoms,suchasthebondsthatholdtogetherthecarbonandhydrogenatomsinmethane(CH4)ortheoxygenandhydrogenatomsinwater(H2O).Inthislessonplan,wewillexplorehowcovalentbondscancontributetotheelectricalconductivityofsolidmaterials.CovalentBondsTounderstandhowcovalentbondscontributetoelectricalconductivity,weneedtofirstunderstandhowcovalentbondsworkingeneral.Whentwoatomscomecloseenoughtogether,theiroutermostelectronsstarttointeractwitheachother.Insomecases,theycanformabondbysharingapairofelectrons.Thisisknownasacovalentbond.Theelectronsthataresharedbetweenthetwoatomsareattractedtobothnucleiandareheldinplacebytheelectrostaticforcesbetweentheprotonsineachnucleusandtheelectrons.Becausetheelectronsaresharedbetweenthetwoatoms,thebondisstrongerthantheforcesthatholdindividualatomstogether,butnotasstrongastheelectrostaticforcesbetweenatomsinanionicbond.Covalentbondsareusuallyformedbetweenatomswithsimilarelectronegativities.Whenanatomhasahigherelectronegativity,itwillattractthesharedelectronsmorestrongly,resultinginapolarcovalentbond.Thismeansthatoneendofthemoleculewillhaveapartialnegativecharge,whiletheotherendwillhaveapartialpositivecharge.SolidConductorsMaterialsthatcanconductelectricityaremadeupofatomsormoleculesthathaveoneormorefreeelectronsthatcanmovethroughthematerial.Thesefreeelectronscancarryelectricalchargefromoneendofthematerialtoanother.Mostmetalsaregoodconductorsofelectricitybecausetheindividualatomsinametallatticelosetheiroutermostelectronstoforma"sea"ofdelocalizedelectrons.Thismeansthatthefreeelectronsarenotassociatedwithanyparticularatomandcanmovearoundthematerialeasily.Solidnon-metals,ontheotherhand,areusuallyinsulatorsbecausetheirvalenceshellsarecompletelyfilledwithelectrons,leavingnofreeelectronstoconductelectricity.Somematerials,however,aresemiconductors,meaningthattheyconductelectricityundercertainconditionsbutnotunderothers.CovalentConductorsSolidmaterialsmadeupofcovalentbondscanalsoconductelectricityiftheyhaveenoughfreeelectrons.Thesefreeelectronscancomefromimpuritiesinthematerial,orfromdefectsinthecrystallatticethatmakeiteasierforelectronstomovearound.Forexample,diamondismadeupentirelyofcovalentbondsandisusuallyapoorconductorofelectricitybecausethevalenceshellsofeachcarbonatomarecompletelyfilled.However,ifdiamondisdopedwithimpuritieslikeboronornitrogen,someofthecarbonatomswillbereplacedbytheseimpurityatoms,creatingextraelectronsthatcanmovearoundthelattice.Siliconisanotherexampleofacovalentconductor.Puresiliconisanelectricalinsulator,butwhendopedwithimpuritieslikearsenicorboron,itbecomesasemiconductorwithfreeelectronsthatcanconductelectricity.ConclusionInconclusion,covalentbondscancontributetotheelectricalconductivityofsolidmaterialsthroughthepresenceoffreeelectronsthatcanmovethroughthematerial.Covalentconductorsareusuallymadeupofmaterialsthathaveimpuritiesordefectsintheircrystallatticethatcancreatefreeelectrons

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