Alkanes and alkenes - chemistry

• Alkanes


  Saturated Hydrocarbons
• Homologous series


  • A group of chemicals that have similar chemical structures
• Alkanes


  • A homologous series of hydrocarbons that contain just carbon and hydrogen atoms only
  • Have the general formula CnH2n+2
• All the atoms in alkanes have formed bonds with as many other atoms as they can, meaning they are saturated
• Alkenes


  Have a C=C double bond
• Alkenes


  • A homologous series of hydrocarbons with one C=C functional group
  • Have the general formula CnH2n
• First three alkenes


  • Ethene
  • Propene
  • Butene
• Alkenes are unsaturated because the double bond can open up, allowing the two carbon atoms to bond with other atoms
• Testing for alkenes


  1. Shake with bromine water

  2. Alkene will decolourise bromine water, turning it from orange to colourless

  3. Alkanes don't react with bromine water as they don't contain double bonds
• Alkenes also react with steam in addition reactions
• Combustion of hydrocarbons


  1. Alkanes and alkenes burn in oxygen

  2. During complete combustion, they are oxidised to form carbon dioxide and water
• In a limited supply of oxygen, you can get incomplete combustion instead