chapter 18—oxidation-reduction reactions：18章氧化还原反应

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1、Chapter18—Oxidation-ReductionReactionsPriceI.Section18.1—OxidationReductionReactionsA.Averycommontypeofreactionwhereelectronsaretransferredfromoneatom(orgroupofatoms)toanother.B.Whenametalandanonmetalreactthemetalgivessomeelectronstothenonmetalandtheyformanioniccompou

2、ndC.Themetalis“oxidized”D.Thenonmetalis“reduced”E.Oxidation=alossofelectronsF.Reduction=againofelectronsII.Section18.2—OxidationStatesA.ElectronTransferismoredifficulttoseewhentheredoxreactioninvolves2ormorenonmetalsB.Tomakethiseasierwegive“imaginary”chargestotheatoms

3、incovalentcompoundsC.OxygenisapartofallredoxreactionsinvolvingnonmetalsD.Oxygen=-2(theperoxideexception!)E.Hydrogen=+1F.Oxidationstatesdependontheelectronegativityoftheatomsinvolved1.Themoreelectronegativeelementalwayscontrolstheelectrons2.Themostelectronegativeelemen

4、tsareF>O>N>ClIII.Section18.3—RedoxReactionsBetweenNonmetalsA.Let’sexaminethecombustionofmethane(CH4)CH4+2O2àCO2+2H2OCH4+2O2àCO2+2H2OB.Pureelementshaveanoxidationnumberof0(zero)C.Weknowoxygenisalwaysa-2andhydrogenisalwaysa+1D.Weusethesefactstodeducetheoxidationnumberso

5、ftherestoftheelementsinthereactionCH4+2O2àCO2+2H2OC=-4H=+1oxygen=0àC=+4oxygen=-2H=+1O=-2E.Noticethattheoxidationnumberofthecarbonincreasesfrom-4to+4…carbonappearstohavelost8electrons.ThemethanehasbeenoxidizedF.Noticethattheoxidationnumberoftheoxygenhasdecreasedfrom0to

6、-2.TheoxygenhasbeenreducedG.Oxidation=anincreaseinoxidationnumberH.Reduction=areductioninoxidationnumberRulesforAssigningOxidationNumbers1.Theoxidationnumberforalluncombinedelementsiszero.2.Theoxidationnumberofasingleionisthesameasitscharge3.Hydrogenhasanoxidationnumb

7、erof+14.Oxygenhasanoxidationnumberof-2(Inperoxidesoxygenisa-1)5.Inbinarycompoundswithouthydrogenoroxygentheatomwiththegreaterectronegativityisassignedthenegativeoxidationnumberbasedonitscharge6.TheoverallchargeofacompoundMUSTBEZERO7.Forpolyatomicions,thesumoftheoxidat

8、ionnumbersmustequaltheoverallchargeI.“OxidizingAgents”and“ReducingAgents”2Na+Cl2à2NaCl1.It’seasytoseethatthesodiumisoxidized