# Pentane (C₅H₁₂) is a member of the alkane homologous series. Explain what is meant by the term 'homologous series' and describe three features that all alkanes share as members of the same homologous series.

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

> Alkanes are saturated hydrocarbons. The first four members of the alkane homologous series are methane (CH₄), ethane (C₂H₆), propane (C₃H₈) and butane (C₄H₁₀).

## Mark scheme (5 marks)

1. A homologous series is a family/group of compounds that share the same general formula (and differ by CH₂ each time)
2. All alkanes contain only carbon and hydrogen atoms (they are hydrocarbons)
3. All alkanes are saturated — they contain only single C–C bonds (no double or triple bonds)
4. Alkanes share the same general formula CₙH₂ₙ₊₂
5. Members of the same homologous series have similar chemical properties (because they share the same functional group / type of bonding)

## 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/pentane-c-h-is-a-member-of-34f0a7f7) · Published by Druglandscape Ltd.