# Pentane (C₅H₁₂) and decane (C₁₀H₂₂) are both simple molecular substances. Pentane has a boiling point of 36 °C whilst decane has a boiling point of 174 °C. Explain why both substances have relatively low boiling points compared to ionic compounds, and why decane has a higher boiling point than pentane.

> Edexcel A-Level Chemistry (9CH0) — 2.4 Forces between molecules · Explain · 5 marks

> Pentane (C₅H₁₂) boiling point: 36 °C. Decane (C₁₀H₂₂) boiling point: 174 °C. Both are simple molecular hydrocarbons.

## Mark scheme (5 marks)

1. Simple molecular substances have weak intermolecular forces (between molecules)
2. Only a small amount of energy is needed to overcome these intermolecular forces
3. Hence the boiling point is low / molecules are easily separated from the liquid
4. Decane has more electrons / is a larger molecule than pentane, so has stronger intermolecular forces
5. More energy is needed to overcome the stronger intermolecular forces in decane, so its boiling point is higher

## Key terms

- [simple molecular substance](https://www.gradenine.co.uk/glossary/simple-molecular-substance)
- [boiling point](https://www.gradenine.co.uk/glossary/boiling-point)

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- [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-and-decane-c-h-are-9b32b4bf) · Published by Druglandscape Ltd.