Methane (CH₄) is the simplest member of the alkane homologous series. Explain two features that show methane belongs to the alkane homologous series.

Eduqas GCSE Chemistry — C7 Organic chemistry · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. Methane contains only single C–C and C–H bonds, so it is saturated, a defining feature of alkanes.
2. Its formula is C₁H₄, which satisfies the general alkane formula CₙH₂ₙ₊₂ (n=1 gives 2×1+2=4).
3. In the homologous series each member differs from the next by a CH₂ group; methane differs from ethane by one CH₂ unit.
4. Alkanes show similar chemical behaviour (e.g. combustion, halogenation under UV) because they share the same functional group, so methane behaves like other alkanes.

Examiner tips

  • Use the exact terms "saturated" and "single bonds". Show the formula calculation for n=1. Mention the CH₂ difference explicitly. Highlight the common reactions of alkanes.

Common mistakes

  • Confusing single bonds with double bonds. Forgetting to calculate 2n+2 for methane. Not stating the CH₂ difference. Using vague phrases like "similar to other hydrocarbons" instead of "alkanes".

Mark scheme (4 marks)

  1. Methane contains only single (C–C or C–H) bonds / alkanes are saturated
  2. Methane has the general formula CₙH₂ₙ₊₂ / fits the general formula of alkanes (CH₄ gives n=1, 2(1)+2=4 ✓)
  3. Alkanes form a homologous series where each successive member differs by CH₂ / methane differs from ethane (C₂H₆) by one CH₂ unit
  4. Members of a homologous series have similar chemical properties / alkanes all react similarly (e.g. combustion / react with halogens in UV light) because they have the same functional group (or lack thereof)

Key terms in this question

homologous series · alkane

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