# But-1-ene and but-2-ene are both members of the alkene homologous series and have the same molecular formula, C₄H₈. State the term used to describe this relationship between but-1-ene and but-2-ene, and explain why both compounds belong to the same homologous series despite having different arrangements of atoms.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 4.4 Alkenes · State and Explain · 4 marks

> But-1-ene has the structural formula CH₂=CHCH₂CH₃. But-2-ene has the structural formula CH₃CH=CHCH₃. Both have the molecular formula C₄H₈.

## Mark scheme (4 marks)

1. The term isomers / isomerism is correctly identified
2. Both compounds have the same functional group (C=C double bond / carbon-carbon double bond)
3. Members of a homologous series have similar chemical properties
4. Both compounds fit / satisfy the general formula CₙH₂ₙ for alkenes

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Chemistry (4CH1)](https://www.gradenine.co.uk/learn)
- [How to answer "State and Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/but-1-ene-and-but-2-ene-are-both-members-b8e5c70d) · Published by Druglandscape Ltd.