AlkanesandAlkenes：烷烃和烯烃

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1、KS4ChemistryAlkanesandAlkenesAlkanesandAlkenesAlkenesAlkanesSummaryactivitiesCombustionofalkanesContentsCrackingandpolymerizationBecausethemainuseofhydrocarbonsisasafuelthereisnopointingoingtotheefforttoseparatethemintoindividualhydrocarbons.Itis,however,possibletoob

2、tainpurehydrocarbonsbyverycarefuldistillation.Thissectionisaboutpurehydrocarbons.PurehydrocarbonsCarbonisanunusualatominthatitisabletoformverystrongcovalentbondswithothercarbonatoms.Whenwethenincludeitsabilitytoalsobondwithotherelementsweopenupthepossibilityofthehigh

3、lydiverseandcomplexmolecules(likeDNA)thathaveledtothepossibilityoflife.Becauseofthis,thechemistryofcarboncontainingcompoundsisoftencalledorganicchemistry.Organicchemistry:carbonThesimplesthydrocarbonsformaseriesofcompoundsknownasalkanes.Theseallconsistofcarbonandhydr

4、ogenonlyandeverycarbonhasfoursinglecovalentbonds.HydrocarbonFormulaStructureMethaneCH4EthaneC2H6PropaneC3H8ButaneC4H10hydrogencarbonAlkanesThenamesofthe4simplestalkanesaremethane,ethane,propaneandbutane.Afterthatthenamesaresystematic(likethewordsusedtodescribegeometr

5、icshapes).E.g.5carbons=pentaneC5H126carbons=hexaneC6H147carbons=heptaneC7H168carbons=octaneC8H189carbons=nonaneC9H2010carbons=decaneC10H22carbonhydrogenpentaneNamesofalkanesAlkanesallhaveverysimilarstructures.Theyallconsistofcarbonandhydrogenonlyandeverycarbonhasfour

6、singlecovalentbonds.TheyhaveaCH3ateachendofthemolecule.WhatdiffersisthenumberofCH2groupsbetweenthetwoends.ItispossibletobuildupaseriesbysimplyaddinganextraCH2groupThisleadstoageneralformulaofCnH2n+2hydrogencarbonn=1n=2n=3n=4StructureofalkanesWhatwillbetheformulaforal

7、kanescontainingthefollowingnumbersofcarbons?C12H26C16H34C31H64C19H40NumberofcarbonsFormula12163119What’stheformula?Althoughnormalchemicalformula-likeC5H12-areusedtodescribealkanes,theydonotconveywhichatomisjoinedtowhichotheratom.Togetaroundthisweoftenuseddisplayedfor

8、mulaetodescribeorganicmolecules.Displayedformulaeshowwhich4atomseachcarbonisbondedto,buteventhesedonotshowtheactual3Dshapes.Forthat