Describe what is meant by a homologous series and state two characteristics that all members of the alkane homologous series share.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
A homologous series is a family of compounds that have the same general formula or the same functional group.
All members of the alkane series differ by a CH₂ unit.
All alkanes have the general formula CₙH₂ₙ₊₂.
All alkanes contain only single C–C and C–H bonds (they are saturated hydrocarbons).
All members of the alkane series differ by a CH₂ unit.
All alkanes have the general formula CₙH₂ₙ₊₂.
All alkanes contain only single C–C and C–H bonds (they are saturated hydrocarbons).
Examiner tips
- Use the definition of a homologous series first. Mention the CH₂ difference. State the general formula and the fact that they are saturated.
- Keep the answer concise – 4 points can be covered in 4 short sentences.
Mark scheme (4 marks)
- A homologous series is a family/group of compounds with the same general formula (or same functional group)
- Each successive member differs by CH₂ (one carbon and two hydrogen atoms)
- All alkanes have the general formula CₙH₂ₙ₊₂
- All alkanes contain only single (C–C and C–H) bonds / are saturated hydrocarbons
Key terms in this question
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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