CIE IGCSE Chemistry

Revision Notes

14.2.1 Alkanes

Alkanes: Properties & Bonding

  • A homologous series of hydrocarbon compounds with only single carbon bonds, there are no C=C bonds present
  • General formula of alkanes:
CnH2n+2
  • Alkanes are classified as saturated hydrocarbons as all the bonds in alkanes are single bonds
  • They are colourless compounds which have a gradual change in their physical properties as the number of carbon atoms in the chain increases
  • Alkanes are generally unreactive compounds but they do undergo combustion reactions, can be cracked into smaller molecules and react with halogens in the presence of light
  • Methane is an alkane and is the major component of natural gas
  • Methane undergoes complete combustion forming carbon dioxide and water:
CH4 + 2O2 → CO2 + 2H2O

The first three alkanes

The-first-three-Alkanes table, IGCSE & GCSE Chemistry revision notes

Extended Only

Substitution Reaction of Alkanes with Halogens

  • In a substitution reaction, one atom is swapped with another atom
  • Alkanes undergo a substitution reaction with halogens in the presence of ultraviolet radiation


Substitution-Alkanes-&-Halogens, IGCSE & GCSE Chemistry revision notes
In the presence of ultraviolet (UV) radiation, methane reacts with bromine in a substitution reaction

 

Methane + Bromine → Bromomethane + Hydrogen Bromide
CH4 + Br2 → CH3Br + HBr

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