化学专业英语

Contents01. THEELEMENTSANDTHEPERIODICTABLE -3-02. THENONMETALELEMENTS -5-03. GROUPSIBANDIIBELEMENTS -7-04. GROUPSIIIB—VIIIBELEMENTS -9-05. INTERHALOGENANDNOBLEGASCOMPOUNDS -11-06. THECLASSIFICATIONOFINORGANICCOMPOUNDS -13-07. THENOMENCLATUREOFINORGANICCOMPOUNDS -15-08. BRONSTED'SANDLEWIS'ACID-BASECONCEPTS -19-09. THECOORDINATIONCOMPLEX -22-10. ALKANES -25-11. UNSATURATEDCOMPOUNDS -28-12. THENOMENCLATUREOFCYCLICHYDROCARBONS -30-13. SUBSTITUTIVENOMENCLATURE -33-14. THECOMPOUNDSCONTAININGOXYGEN -37-15. PREPARATIONOFACARBOXYLiCACIDBYTHEGRIGNARDMETHOD -39-16. THESTRUCTURESOFCOVALENTCOMPOUNDS -41-17. OXIDATIONANDREDUCTIONINORGANICCHEMISTRY -44-18. SYNTHESISOFALCOHOLSANDDESIGNOFORGANICSYNTHESIS -47-19. ORGANOMETALLICS—METALπCOMPLEXES -49-20. THEROLEOFPROTECTIVEGROUPSINORGANICSYNTHESIS -52-21. ELECTROPHILICREACTIONSOFAROMATICCOMPOUNDS -54-22. POLYMERS -57-23. ANALYTICALCHEMISTRYANDPROBLEMSINSOCIETY -61-24. VOLUMETRICANALYSIS -63-25. QUALITATIVEORGANICANALYSIS -65-26. VAPOR-PHASECHROMATOGRAPHY -67-27. INFRAREDSPECTROSCOPY -70-28. NUCLEARMAGNETICRESONANCE(I) -72-29. NUCLEARMAGNETICRESONANCE(II) -75-30. AMAPOFPHYSICALCHEMISTRY -77-31. THECHEMICALTHERMODYNAMICS -79-32. CHEMICALEQUILIBRIUMANDKINETICS -82-33. THERATESOFCHEMICALREACTIONS -85-34. NATUREOFTHECOLLOIDALSTATE -88-35. ELECTROCHEMICALCELLS -90-36. BOILINGPOINTSANDDISTILLATION -93-37. EXTRACTIVEANDAZEOTROPICDISTILLATION -96-38. CRYSTALLIZATION -98-39. MATERIALACCOUNTING -100-40. THELITERATUREMATRIXOFCHEMISTRY -102-

THEELEMENTSANDTHEPERIODICTABLEThenumberofprotonsinthenucleusofanatomisreferredtoastheatomicnumber,orprotonnumber,Z.Thenumberofelectronsinanelectricallyneutralatomisalsoequaltotheatomicnumber,Z.Thetotalmassofanatomisdeterminedverynearlybythetotalnumberofprotonsandneutronsinitsnucleus.Thistotaliscalledthemassnumber,A.Thenumberofneutronsinanatom,theneutronnumber,isgivenbythequantityA-Z.Thetermelementrefersto,apuresubstancewithatomsallofasinglekind.Tothechemistthe"kind"ofatomisspecifiedbyitsatomicnumber,sincethisisthepropertythatdeterminesitschemicalbehavior.AtpresentalltheatomsfromZ=1toZ=107areknown;thereare107chemicalelements.Eachchemicalelementhasbeengivenanameandadistinctivesymbol.FormostelementsthesymbolissimplytheabbreviatedformoftheEnglishnameconsistingofoneortwoletters,forexample:oxygen==Onitrogen==Nneon==Nemagnesium==MgSomeelements,whichhavebeenknownforalongtime,havesymbolsbasedontheirLatinnames,forexample:iron==Fe(ferrum)copper==Cu(cuprum)lead==Pb(plumbum)AcompletelistingoftheelementsmaybefoundinTable1.BeginninginthelateseventeenthcenturywiththeworkofRobertBoyle,whoproposedthepresentlyacceptedconceptofanelement,numerousinvestigationsproducedaconsiderableknowledgeofthepropertiesofelementsandtheircompounds1.In1869,D.MendeleevandL.Meyer,workingindependently,proposedtheperiodiclaw.Inmodernform,thelawstatesthatthepropertiesoftheelementsareperiodicfunctionsoftheiratomicnumbers.Inotherwords,whentheelementsarelistedinorderofincreasingatomicnumber,elementshavingcloselysimilarpropertieswillfallatdefiniteintervalsalongthelist.Thusitispossibletoarrangethelistofelementsintabularformwithelementshavingsimilarpropertiesplacedinverticalcolumns2.SuchanarrangementiscalledaperiodicEachhorizontalrowofelementsconstitutesaperiod.Itshouldbenotedthatthelengthsoftheperiodsvary.Thereisaveryshortperiodcontainingonly2elements,followedbytwoshortperiodsof8elementseach,andthentwolongperiodsof18elementseach.Thenextperiodincludes32elements,andthelastperiodisapparentlyincomplete.Withthisarrangement,elementsinthesameverticalcolumnhavesimilarcharacteristics.Thesecolumnsconstitutethechemicalfamiliesorgroups.Thegroupsheadedbythemembersofthetwo8-elementperiodsaredesignatedasmaingroupelements,andthemembersoftheothergroupsarecalledtransitionorinnertransitionelements.Intheperiodictable,aheavysteppedlinedividestheelementsintometalsandnonmetals.Elementstotheleftofthisline(withtheexceptionofhydrogen)aremetals,whilethosetotherightarenonmetals.Thisdivisionisforconvenienceonly;elementsborderingtheline—themetalloids-havepropertiescharacteristicof-bothmetalsandnonmetals.Itmaybeseenthatmostoftheelements,includingallthetransitionandinnertransitionelements,aremetals.Exceptforhydrogen,agas,theelementsofgroupIAmakeupthealkalimetalfamily.Theyareveryreactivemetals,andtheyareneverfoundintheelementalstateinnature.However,theircompoundsarewidespread.Allthemembersofthealkalimetalfamily,formionshavingachargeof1+only.Incontrast,theelementsofgroupIB—copper,silver,andgold—arecomparativelyinert.Theyaresimilartothealkalimetalsinthattheyexistas1+ionsinmanyoftheircompounds.However,asischaracteristicofmosttransitionelements,theyformionshavingotherchargesaswell.TheelementsofgroupIIAareknownasthealkalineearthmetals.Theircharacteristicionicchargeis2+.Thesemetals,particularlythelasttwomembersofthegroup,arealmostasreactiveasthealkalimetals.ThegroupIIBelements—zinc,cadmium,andmercuryarelessreactivethanarethoseofgroupIIA5,butaremorereactivethantheneighboringelementsofgroupIB.Thecharacteristicchargeontheirionsisalso2+.Withtheexceptionofboron,groupIIIAelementsarealsofairlyreactivemetals.Aluminumappearstobeinerttowardreactionwithair,butthisbehaviorstemsfromthefactthatthemetalformsathin,invisiblefilmofaluminumoxideonthesurface,whichprotectsthebulkofthemetalfromfurtheroxidation.ThemetalsofgroupIIIAformionsof3+charge.GroupIIIBconsistsofthemetalsscandium,yttrium,lanthanum,andactinium.GroupIVAconsistsofanonmetal,carbon,twometalloids,siliconandgermanium,andtwometals,tinandlead.EachoftheseelementsformssomecompoundswithformulaswhichindicatethatfourotheratomsarepresentpergroupIVAatom,as,forexample,carbontetrachloride,GCl4.ThegroupIVBmetals—titanium,zirconium,andhafnium—alsoformscompoundsinwhicheachgroupIVBatomiscombinedwithfourotheratoms;thesecompoundsarenonelectrolyteswhenpure.TheelementsofgroupVAincludethreenonmetals—nitrogen,phosphorus,andarsenic—andtwometals—antimonyandbismuth.AlthoughcompoundswiththeformulasN2O5,PCl5,andAsCl5exist,noneofthemisionic.Theseelementsdoformcompounds-nitrides,phosphides,andarsenides—inwhichionshavingchargesofminusthreeoccur.TheelementsofgroupVBareallmetals.Theseelementsformsuchavarietyofdifferentcompoundsthattheircharacteristicsarenoteasilygeneralized.Withtheexceptionofpolonium,theelementsofgroupVIAaretypicalnonmetals.Theyaresometimesknown,asthe,chalcogens,fromtheGreekwordmeaning"ashformers".Intheirbinarycompoundswithmetalstheyexistasionshavingachargeof2-.TheelementsofgroupⅦAareallnonmetalsandareknownasthehalogens.fromtheGreektermmeaning"saltformers.”Theyarethemostreactivenonmetalsandarecapableofreactingwithpracticallyallthemetalsandwithmostnonmetals,includingeachother.TheelementsofgroupsⅥB,ⅦB,andVIIIBareallmetals.TheyformsuchawideVarietyofcompoundsthatitisnotpracticalatthispointtopresentanyexamplesasbeingtypicalofthebehavioroftherespectivegroups.Theperiodicityofchemicalbehaviorisillustratedbythefactthat.excludingthefirstperiod,eachperiodbeginswithaveryreactivemetal.Successiveelementalongtheperiodshowdecreasingmetalliccharacter,eventuallybecomingnonmetals,andfinally,ingroupⅦA,averyreactivenonmetalisfound.Eachperiodendswithamemberofthenoblegasfamily.

THENONMETALELEMENTSWenotedearlier.that-nonmetalsexhibitpropertiesthataregreatlydifferentfromthoseofthemetals.Asarule,thenonmetalsarepoorconductorsofelectricity(graphiticcarbonisanexception)andheat;theyarebrittle,areoftenintenselycolored,andshowanunusuallywiderangeofmeltingandboilingpoints.Theirmolecularstructures,usuallyinvolvingordinarycovalentbonds,varyfromthesimplediatomicmoleculesofH2,Cl2,I2,andN2tothegiantmoleculesofdiamond,siliconandboron.Thenonmetalsthataregasesatroomtemperaturearethelow-molecularweightdiatomicmoleculesandthenoblegasesthatexertverysmallintermolecularforces.Asthemolecularweightincreases,weencounteraliquid(Br2)andasolid(I2)whosevaporpressuresalsoindicatesmallintermolecularforces.CertainpropertiesofafewnonmetalsarelistedinTable2.Table2-MolecularWeightsandMeltingPointsofCertainNonmetalsDiatomicMoleculesMolecularWeightMeltingPoint°CColorH22-239.1'NoneN228-210NoneF238-223PaleyellowO232-218PaleblueCl271-102Yellow—greenBr2160-7.3Red—brownI2254113Gray—blackSimplediatomicmoleculesarenotformedbytheheaviermembersofGroupsVandVIatordinaryconditions.Thisisindirectcontrasttothefirstmembersofthesegroups,N2andO2.Thedifferencearisesbecauseofthelowerstabilityofπbondsformedfromporbitalsofthethirdandhighermainenergylevelsasopposedtothesecondmainenergylevel2.Thelargeratomicradiiandmoredenseelectroncloudsofelementsofthethirdperiodandhigherdonotallowgoodparalleloverlapofporbitalsnecessaryforastrongπbond.Thisisageneralphenomenon—strongπbondsareformedonlybetweenelementsofthesecondperiod.Thus,elementalnitrogenandoxygenformstablemoleculeswithbothσandπbonds,butothermembersoftheirgroupsformmorestablestructuresbasedonσbondsonlyatordinaryconditions.Note3thatGroupVIIelementsformdiatomicmolecules,butπbondsarenotrequiredforsaturationofvalence.Sulfurexhibitsallotropicforms.Solidsulfurexistsintwocrystallineformsandinanamorphousform.Rhombicsulfurisobtainedbycrystallizationfromasuitablesolution,suchasCS2,anditmeltsat112°C.Monoclinicsulfurisformedbycoolingmeltedsulfuranditmeltsat119°C.BothformsofcrystallinesulfurmeltintoS-gamma,whichiscomposedofS8molecules.TheS8moleculesarepuckeredringsandsurviveheatingtoabout160°C.Above160°C,theS8ringsbreakopen,andsomeofthesefragmentscombinewitheachothertoformahighlyviscousmixtureofirregularlyshapedcoils.Atarangeofhighertemperaturestheliquidsulfurbecomessoviscousthatitwillnotpourfromitscontainer.Thecoloralsochangesfromstrawyellowatsulfur'smeltingpointtoadeepreddish-brownasitbecomesmoreviscous.As4theboilingpointof444°Cisapproached,thelarge-coiledmoleculesofsulfurarepartiallydegradedandtheliquidsulfurdecreasesinviscosity.Ifthehotliquidsulfurisquenchedbypouringitintocoldwater,theamorphousformofsulfurisproduced.Thestructureofamorphoussulfurconsistsoflarge-coiledheliceswitheightsulfuratomstoeachturnofthehelix;theoverallnatureofamorphoussulfurisdescribedas3rubberybecauseitstretchesmuchlikeordinaryrubber.Inafewhourstheamorphoussulfurrevertstosmallrhombiccrystalsanditsrubberypropertydisappears.Sulfur,animportantrawmaterialinindustrialchemistry,occursasthefreeelement,asSO2involcanicregions,asH2Sinmineralwaters,andinavarietyofsulfideoressuchasironpyriteFeS2,zincblendeZnS,galenaPbSandsuch,andincommonformationsofgypsumCaSO4•2H2O,anhydriteCaSO4,andbarytesBaSO4•2H2O.Sulfur,inoneformoranother,isusedinlargequantitiesformakingsulfuricacid,fertilizers,insecticides,andpaper.SulfurintheformofSO2obtainedintheroastingofsulfideoresisrecoveredandconvertedtosulfuricacid,althoughinpreviousyearsmuchofthisSO2wasdiscardedthroughexceptionallytallsmokestacks.Fortunately,itisnoweconomicallyfavorabletorecoverthesegases,thusgreatlyreducingthistypeofatmosphericpollution.Atypicalroastingreactioninvolvesthechange:2ZnS+3O2—2ZnO+2SO2Phosphorus,below800℃consistsoftetratomicmolecules,P4.Itsmolecularstructureprovidesforacovalenceofthree,asmaybeexpectedfromthethreeunpairedpelectronsinitsatomicstructure,andeachatomisattachedtothreeothers6.Insteadofastrictlyorthogonalorientation,withthethreebonds90°toeachother,thebondanglesareonly60°.Thissupposedlystrainedstructureisstabilizedbythemutualinteractionofthefouratoms(eachatomisbondedtotheotherthree),butitischemicallythemostactiveformofphosphorus.Thisformofphosphorus,thewhitemodification,isspontaneouslycombustibleinair.Whenheatedto260°Citchangestoredphosphorus,whosestructureisobscure.Redphosphorusisstableinairbut,likeallformsofphosphorus,itshouldbehandledcarefullybecauseofitstendencytomigratetotheboneswheningested,resultinginseriousphysiologicaldamage.Elementalcarbonexistsinoneoftwocrystallinestructures—diamondandgraphite.Thediamondstructure,basedontetrahedralbondingofhybridizedsp3orbitals,isencounteredamongGroupIVelements.Wemayexpectthatasthebondlengthincreases,thehardnessofthediamond-typecrystaldecreases.Althoughthetetrahedralstructurepersistsamongtheelementsinthisgroup—carbon,silicon,germanium,andgraytin—theinteratomicdistancesincreasefrom1.54Aforcarbonto2.80Aforgraytin.Consequently.thebondstrengthsamongthefourelementsrangefromverystrongtoquiteweak.Infact,graytinissosoftthatitexistsintheformofmicrocrystalsormerelyasapowder.TypicaloftheGroupIVdiamond-typecrystallineelements,itisanonconductorandshowsothernonmetallicproperties7.

GROUPSIBANDIIBELEMENTSPhysicalpropertiesofGroupIBandIIBTheseelementshaveagreaterbulkuseasmetalsthanincompounds,andtheirphysicalpropertiesvarywidely.Goldisthemostmalleableandductileofthemetals.Itcanbehammeredintosheetsof0.00001inchinthickness;onegramofthemetalcanbedrawnintoawire1.8miinlength1.Copperandsilverarealsometalsthataremechanicallyeasytowork.Zincisalittlebrittleatordinarytemperatures,butmayberolledintosheetsatbetween120°to150℃;itbecomesbrittleagainabout200℃-Thelow-meltingtemperaturesofzinccontributetothepreparationofzinc-coatediron.galvanizediron;cleanironsheetmaybedippedintovatsofliquidzincinitspreparation.Adifferentprocedureistosprinkleorairblastzincdustontohotironsheetingforazincmeltandthencoating.Cadmiumhasspecificusesbecauseofitslow-meltingtemperatureinanumberofalloys.Cadmiumrodsareusedinnuclearreactorsbecausethemetalisagoodneutronabsorber.Mercuryvaporanditssaltsarepoisonous,thoughthefreemetalmaybetakeninternallyundercertainconditions.Becauseofitsrelativelylowboilingpointandhencevolatilenature,freemercuryshouldneverbeallowedtostandinanopencontainerinthelaboratory.Evidenceshowsthatinhalationofitsvaporsisinjurious.Themetalalloysreadilywithmostofthemetals(exceptironandplatinum)toformamalgams,thenamegiventoanyalloyofmercury.Coppersulfate,orbluevitriol(CuSO4•5H2O)isthemostimportantandwidelyusedsaltofcopper.Onheating,thesaltslowlyloseswatertoformfirstthetrihydrate(CuSO4•3HzO),thenthemonohydrate(CuSO4•H2O),andfinallythewhiteanhydroussalt.Theanhydroussaltisoftenusedtotestforthepresenceofwaterinorganicliquids.Forexample,someoftheanhydrouscoppersaltaddedtoalcohol(whichcontainswater)willturnbluebecauseofthehydrationofthesalt.Coppersulfateisusedinelectroplating.Fishermendiptheirnetsincoppersulfatesolutiontoinhibitthegrowthoforganismsthatwouldrotthefabric.Paintsspecificallyformulatedforuseonthebottomsofmarinecraftcontaincoppercompoundstoinhibitthegrowthofbarnaclesandotherorganisms.Whendiluteammoniumhydroxideisadded"toasolutionofcopper(I)ions,agreenishprecipitateofCu(OH)2orabasiccopper(I)saltisformed.Thisdissolvesasmoreammoniumhydroxideisadded.Theexcessammoniaformsanammoniatedcomplexwiththecopper(I)ionofthecomposition,Cu(NH3)42+.Thisionisonlyslightlydissociated;henceinanammoniacalsolutionveryfewcopper(I)ionsarepresent.Insolublecoppercompounds,execptcoppersulfide,aredissolvedbyammoniumhydroxids.Theformationofthecopper(I)ammoniaionisoftenusedasatestforCu2+becauseofitsdeep,intensebluecolor.Copper(I)ferrocyanide[Cu2Fe(CN)6]isobtainedasareddish-brownprecipitateontheadditionofasolubleferrocyanidetoasolutionofcopper(I)ions.Theformationofthissaltisalsousedasatestforthepresenceofcopper(I)ions.CompoundsofSilverandGoldSilvernitrate,sometimescalledlunarcaustic,isthemostimportantsaltofsilver.Itmeltsreadilyandmaybecastintosticksforuseincauterizingwounds.Thesaltispreparedbydissolvingsilverinnitricacidandevaporatingthesolution.3Ag+4HNO3—3AgNO3+NO+2H2OThesaltisthestartingmaterialformostofthecompoundsofsilver,includingthehalidesusedinphotography.Itisreadilyreducedbyorganicreducingagents,withtheformationofablackdepositoffinelydividedsilver;thisactionisresponsibleforblackspotsleftonthefingersfromthehandlingofthesalt.Indeliblemarkinginksandpencilstakeadvantageofthispropertyofsilvernitrate.Thehalidesofsilver,exceptthefluoride,areveryinsolublecompoundsandmaybeprecipitatedbytheadditionofasolutionofsilversalttoasolutioncontainingchloride,bromide,oriodideions.Theadditionofastrongbasetoasolutionofasilversaltprecipitatesbrownsilveroxide(Ag2G).Onemightexpectthehydroxideofsilvertoprecipitate,butitseemslikelythatsilverhydroxideisveryunstableandbreaksdownintotheoxideandwater—if,indeed,itiseverformedatall3.However,sinceasolutionofsilveroxidejsdefinitelybasic,theremustbehydroxideionspresentinsolution.Ag2O+H2O=2Ag++2OH-Becauseofitsinactivity,goldformsrelativelyfewcompounds.Twoseriesofcompoundsareknown—monovalentandtrivalent.Monovalent(aurous)compoundsresemblesilvercompounds(aurouschlorideiswaterinsolubleandlightsensitive),whilethehighervalence(auric)compoundstendtoformcomplexes.Goldisresistanttotheactionofmostchemicals—air,oxygen,andwaterhavenoeffect.Thecommonacidsdonotattackthemetal,butamixtureofhydrochloricandnitricacids(aquaregia)dissolvesittoformgold(I)chlorideorchloroauricacid.Theactionisprobablyduetofreechlorinepresentintheaquaregia.3HCl+HNO3→NOCl+Cl2+2H2O2Au+3Cl2→2AuCl3AuCl3+HCl→HAuCl4chloroauricacid(HAuCl4-H2Ocrystallizesfromsolution).CompoundsofZincZincisfairlyhighintheactivityseries.Itreactsreadilywithacidstoproducehydrogenanddisplaceslessactivemetalsfromtheirsalts.1heactionofacidsonimpurezincismuchmorerapidthanonpurezinc,sincebubblesofhydrogengascollectonthesurfaceofpurezincandslowdowntheaction.Ifanothermetalispresentasanimpurity,thehydrogenisliberatedfromthesurfaceofthecontaminatingmetalratherthanfromthezinc.AnelectriccoupletofacilitatetheactionisprobablySetupbetweenthetwometals.Zn+2H+→Zn2++H2Zincoxide(ZnO),themostwidelyusedzinccompound,isawhitepowderatordinarytemperatures,butchangestoyellowonheating.Whencooled,itagainbecomeswhite.Zincoxideisobtainedbyburningzincinair,byheatingthebasiccarbonate,orbyroastingthesulfide.TheprincipaluseofZnOisasafillerinrubbermanufacture,particularlyinautomobiletires.Asabodyforpaintsithastheadvantageoverwhiteleadofnotdarkeningonexposuretoanatmospherecontaininghydrogensulfide.Itscoveringpower,however,isinferiortothatofwhitelead.

GROUPSIIIB—VIIIBELEMENTSGroupI-Bincludestheelementsscandium,yttrium,lanthanum,andactinium1,andthetworare-earthseriesoffourteenelementseach2—thelanthanideandactinideseries.Theprincipalsourceoftheseelementsisthehighgravityriverandbeachsandsbuiltupbyawater-sortingprocessduringlongperiodsofgeologictime.Monazitesand,whichcontainsamixtureofrareearthphosphates,andanyttriumsilicateinaheavysandarenowcommercialsourcesofanumberofthesescarceelements.Separationoftheelementsisadifficultchemicaloperation.Thesolubilitiesoftheircompoundsaresonearlyalikethataseparationbyfractionalcrystallizationislaboriousandtime-consuming.Inrecentyears,ionexchangeresinsinhighcolumnshaveprovedeffective.WhencertainacidsareallowedtoflowdownslowlythroughacolumncontainingaresintowhichionsofGroupIIIBmetalsareadsorbed,ionsaresuccessivelyreleasedfromtheresin3.Theresultingsolutionisremovedfromthebottomofthecolumnortowerinbandsorsections.Successivesectionswillcontainspecificionsintheorderofreleasebytheresin.Forexample.lanthanumion(La3+)ismosttightlyheldtotheresinandisthelasttobeextracted,lutetiumion(Lu3+)islesstightlyheldandappearsinoneofthefirstsectionsremoved.Ifthesolutionsarerecycledandtheacidconcentrationscarefullycontrolled,veryeffectiveseparationscanbeaccomplished.Quantitiesofallthelanthanideseries(exceptpromethium,Pm,whichdoesnotexistinnatureasastableisotope)areproducedforthechemicalmarket.Thepredominantgroupoxidationnumberofthelanthanideseriesis+3,butsomeoftheelementsexhibitvariableoxidationstates.Ceriumformscerium(III)andcerium(IV)sulfates,Ce2(SO4)3andCe(SO4)2,whichareemployedincertainoxidation-reductiontitrations.Manyrareearthcompoundsarecoloredandareparamagnetic,presumablyasaresultofunpairedelectronsinthe4forbitals.Allactinideelementshaveunstablenucleiandexhibitradioactivity.Thosewithhigheratomicnumbershavebeenobtainedonlyintraceamounts.Actinium(89Ac),likelanthanum,isaregularGroupIIIBelement.GroupIVBElementsInchemicalpropertiestheseelementsresemblesilicon,buttheybecomeincreasinglymoremetallicfromtitaniumtohafnium.Thepredominantoxidationstateis+4and,aswithsilica(SiO2),theoxidesoftheseelementsoccurnaturallyinsmallamounts.TheformulasandmineralnamesoftheoxidesareTiO2,rutile;ZrO2,zirconia;HfO2,hafnia.Titaniumismoreabundantthanisusuallyrealized.Itcomprisesabout0.44%oftheearth'scrust.Itisover5.0%inaveragecompositionoffirstanalyzedmoonrock.Zirconiumandtitaniumoxidesoccurinsmallpercentagesinbeachsands.Titaniumandzirconiummetalsarepreparedbyheatingtheirchlorideswithmagnesiummetal.Bothareparticularlyresistanttocorrosionandhavehighmeltingpoints.PureTiO2isaverywhitesubstancewhichistakingtheplaceofwhiteleadinmanypaints.Three-fourthsoftheTiO2isusedinwhitepaints,varnishes,andlacquers.Ithasthehighestindexofrefraction(2.76)andthegreatesthidingpowerofallthecommonwhitepaintmaterials.TiO2alsoisusedinthepaper,rubber,linoleum,leather,andtextileindustries.GroupVBElements:Vanadium,Niobium,andTantalumThesearetransitionelementsofGroupVB,withapredominantoxidationnumberof+5.Theiroccurrenceiscomparativelyrare.Thesemetalscombinedirectlywithoxygen,chlorine,andnitrogentoformoxides,chlorides,andnitrides,respectively.Asmallpercentageofvanadiumalloyedwithsteelgivesahightensilestrengthproductwhichisverytoughandresistanttoshockandvib