# Methane and ethane are both alkanes. Describe the similarities and differences in their molecular structures, and explain what is meant by calling them a homologous series.

> WJEC A-Level Chemistry (Wales) — 2.5 Hydrocarbons · Describe · 5 marks

> Methane has the molecular formula CH₄. Ethane has the molecular formula C₂H₆.

## Mark scheme (5 marks)

1. Both methane and ethane contain only carbon and hydrogen atoms (are hydrocarbons)
2. Both molecules contain only single (C–C or C–H) bonds / are saturated
3. Methane has one carbon atom whereas ethane has two carbon atoms (they differ by one CH₂ unit)
4. A homologous series is a family of compounds that share the same general formula (CₙH₂ₙ₊₂ for alkanes)
5. Members of a homologous series have similar chemical properties but gradually changing physical properties (e.g. boiling point increases as chain length increases)

## Key terms

- [alkane](https://www.gradenine.co.uk/glossary/alkane)
- [homologous series](https://www.gradenine.co.uk/glossary/homologous-series)

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/methane-and-ethane-are-both-alkanes-d460395d) · Published by Druglandscape Ltd.