Methane is the simplest alkane and is the main component of natural gas. Explain why methane is classified as an organic compound and describe the bonding and general formula that are characteristic of all alkanes.

WJEC A-Level Chemistry (Wales) — 2.4 Organic compounds · Explain · 5 marks · View as Markdown

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

Natural gas is used as a fuel in homes and industry. Its main component, methane, belongs to the homologous series of alkanes.

Model answer (5 marks)

Methane is classified as an organic compound because it contains carbon, the defining element of organic chemistry.

Alkanes are saturated hydrocarbons that contain only single (covalent) bonds between carbon atoms. Each carbon atom is tetravalent, forming four single bonds – either C–C or C–H.

The general formula for alkanes is CₙH₂ₙ₊₂, reflecting that they are saturated and contain no double or triple bonds.

Examiner tips

  • Use the word ‘carbon’ to justify organic classification. State that alkanes have only C–C single bonds and C–H bonds. Give the general formula CₙH₂ₙ₊₂ and explain it is saturated.
  • common_mistakes
  • :
  • Saying ‘organic compounds contain hydrogen’ instead of carbon. Forgetting that alkanes are saturated (i.e. no double bonds).

Mark scheme (5 marks)

  1. Methane (and all organic compounds) contain carbon / organic compounds are compounds that contain carbon
  2. Alkanes contain only single (covalent) bonds between carbon atoms / C–C single bonds
  3. Each carbon atom forms four bonds / carbon is tetravalent / all bonds in alkanes are C–H or C–C single bonds
  4. The general formula of alkanes is CₙH₂ₙ₊₂
  5. Alkanes are saturated / they are saturated hydrocarbons / no double bonds so they are saturated

Key terms in this question

organic compound · alkane · general formula

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