高中化学竞赛辅导 无机化学 20.doc

§20-2锕系元素TheActinides我们只介绍铀及其化合物的性质。铀的重要化合物UO2（暗棕色）U3O8（墨绿色）UO3（橙黄色）一、铀的氧化物1．UO3(1)amphotericoxide(2)decomposition2UO32UO2+O2(3)preparation2UO2(NO3)22UO3+4NO2+O22．U3O8preparation：3U(C2O4)2U3O8+8CO+4CO2或者：3U+4O2U3O8U3O8不溶于水，但溶于酸，生成。二、硝酸铀酰[UO2(NO3)2]1.PreparationUO3+2HNO3UO2(NO3)2+H2O2.Properties水解生成加碱生成Na2U2O7·6H2O（黄色），加热脱水，生成无水Na2U2O7，俗称铀黄。3.StructureUO2(NO3)2·2H2O（六角双锥）三、UF6（八面体）1.PreparationUO3+3SF4UF6+3SOF2Fig.20.1ThestructureofUO2(NO3)2·2H2O2.HydrolysisUF6+2H2OUO2F2+4HFSuperconductivityH.KammerlingOnnes(NobelPrizeforPhysics,1913)discoveredsuperconductivityinLeidenin1911whenhecooledmercurytothetemperatureofliquidhelium;Manyothermaterials,mostlymetalsandalloys,weresubsequentlyfoundtodisplaysuperconductivityatverylowtemperatures.Twopropertiescharacterizeasuperconductor:1.Itisperfectlyconducting,i.e.ithaszeroresistance.2.Itisperfectlydiamagnetic,i.e.itcompletelyexcludesappliedmagneticfields.ThisistheMeissnereffectandisthereasonwhyasuperconductorcanlevitateamagnet.Superconductivityexistswithintheboundariesofthreelimitingparameterswhichmustnotbeexceeded：thecriticaltemperature(Tc),thecriticalmagneticfield(Hc)andthecriticalcurrentdensity(Jc).Until1986thehighestrecordedvalueofTcwas~23KforNb3GebutinthatyearBednorzandMuller,inpioneeringworkforwhichtheyreceivedthe1987NobelPrizeforPhysics,reportedTc=30KinanentirelynewBa-La-Cu-OceramicsystemquicklyidentifiedasLa2-xBaxCuO4.ThispromptedanexaminationofotherCu-Osystemsandthetechnologicallyimportantbreakthroughin1987bytheHoustonandAlabamateamsofC.W.ChuandM.K.Wu,ofsuperconductivityattemperaturesattainableinliquidnitrogen,Tc=95KinamaterialsubsequentlyshowntobeYBa2Cu3O7,“YBCO".This,andothermaterialsinwhichYisreplacedbyalanthanide,arereferredtoas"1,2,3"materialsbecauseoftheirstoichiometry.Thisproducedaquiteunprecedentedexplosionofactivityamongstchemists,physicistsandmaterialscientistsaroundtheworld.ThoughthehighestTchasbeenpushedupto135K(or164Kunder350kbarpressure)inHgBa2Ca2Cu3O8,YBCOisstillthearchetypalhightemperaturesuperconductor.I