# Methane, ethane, propane and butane are all members of the alkane homologous series. Explain what is meant by a homologous series and describe three properties that all alkanes share as a result of belonging to the same homologous series.

> Edexcel A-Level Chemistry (9CH0) — 6.1 Introduction to organic chemistry · Explain · 5 marks

> Alkanes are the simplest organic compounds and are found in crude oil. Their general formula is CₙH₂ₙ₊₂.

## Mark scheme (5 marks)

1. A homologous series is a family/group of compounds that share the same general formula
2. Members of a homologous series differ by one CH₂ unit (a methylene group) between successive members
3. All alkanes have similar chemical properties / react in similar ways (e.g. undergo combustion)
4. Alkanes are saturated hydrocarbons / contain only single C–C and C–H bonds / contain no carbon-carbon double bonds
5. Alkanes show a gradual trend in physical properties such as boiling point / melting point / viscosity increasing as the number of carbon atoms increases

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/methane-ethane-propane-and-butane-are-66e06393) · Published by Druglandscape Ltd.