Organic Chemistry - Alkenes & -kanes

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  • Created by: Elena R
  • Created on: 16-08-15 19:05
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  • Organic Chem
    • WHAT ARE ALKANES?
      • they are HYDROCARBONS
        • Hydrocarbons are molecules that are made up of hydrogen and carbon atoms only
        • they are part of the same HOMOLOGOUS SERIES
          • (a group of compounds that can all be represented by the same general formula)
          • Alkanes all have the general formula  CnH2n+2
            • So if BUTANE has 4 carbons, it's got to have (2x4)+2=10 hydrogens
    • WHAT ARE ALKENES
      • Alkenes are another type of HYDROCARBON. They're different from alkanes because they contain double bonds.
        • All alkenes have the general formula CnH2n
          • (they have twice as many hydrogens as carbons)
        • Untitled
        • Therefore, they are UNSATURATED MOLECULESBECAUSE THEY CAN MAKE MORE BONDS - the double bond can open up, allowing the 2 carbon atoms to bond with other atoms
    • Combustion of ALKANES
      • INCOMPLETE
        • NOT SAFE!!
          • if there isn't enough oxygen, alkane combustion will be INCOMPLETE
          • alkane + oxygen = carbon + carbon monoxide + carbon dioxide + water
          • because CARBON and CARBON MONOXIDE (poisonous gas) are produced too
          • Makes a smoky yellow flame and less energy than complete combustion
      • COMPLETE
        • happens when there's plenty of oxygen about. Alkanes burn to produce CARBON DIOXIDE and WATER
        • alkane + oxygen= carbon dioxide+ water
          • this releases lots of energy!
            • and 2 harmless waste products
          • The gas will burn with a CLEAN, BLUE FLAME
        • eg; complete combustion of METHANE: CH4 +2O2=CO2 + 2H2O
    • HALOGENS REACT WITH ALKANES TO MAKE HALOALKANES
      • produced when Halogens react with alkanes IN THE PRESENCE OF ULTRAVIOLET LIGHT
        • in these reactions a HYDROGEN ATOM from the ALKANE is REPLACED (substituted) by CHLORINE OR BROMINE
          • There fore, it is called a SUBSTITUTION REACTION
          • Eg; methane + bromine = bromomethane + hydrogen bromide
            • CH4  +  Br = CH3Br  +  HBr
    • HALOGENS REACT WITH ALKENES FORMING HALOALKANES
      • These are called ADDITION REACTIONS because the C=C double bond is SPLIT and a HALOGEN ATOM is added to EACH OF THE CARBONS
        • eg; Bromine and Ethene react together to form DIBROMOETHANE
        • The reaction between bromine and alkenes is used as a TEST for CARBON-CARBON DOUBLE BONDS
          • When you shake an Alkene with ORANGE BROMINE WATER, the solution becomes COLOURLESS - this is because he b
          • Bromine water is used to tell the difference between an alkane and an alkene. An alkene will turn orange bromine water colourless as it reacts with the double bond. Bromine water remains brown in the presence of an alkane as there is no double bond

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