# Methane (CH₄) is a covalently bonded molecule with a tetrahedral shape and bond angles of 109.5°. Carbon dioxide (CO₂) is also a covalently bonded molecule, but it has a linear shape with bond angles of 180°. Explain why methane has a tetrahedral shape and why carbon dioxide has a linear shape.

> Edexcel A-Level Chemistry (9CH0) — 2.2 Covalent bonding and shapes · Explain · 5 marks

> Methane (CH₄) contains one carbon atom bonded to four hydrogen atoms. Carbon dioxide (CO₂) contains one carbon atom bonded to two oxygen atoms, each by a double bond. Neither molecule contains lone pairs on the central atom.

## Mark scheme (5 marks)

1. Covalent bonds are formed by the sharing of a pair of electrons between two atoms
2. In methane, there are four pairs of electrons (four bonding pairs) around the central carbon atom
3. The four electron pairs in methane repel each other and arrange themselves as far apart as possible, giving a tetrahedral shape with bond angles of 109.5°
4. In carbon dioxide, there are only two bonding regions / two double bonds around the central carbon atom
5. The two electron pairs / bonding regions in carbon dioxide repel each other and arrange as far apart as possible, giving a linear shape with bond angles of 180°

## Key terms

- [tetrahedral](https://www.gradenine.co.uk/glossary/tetrahedral)
- [linear](https://www.gradenine.co.uk/glossary/linear)

## 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-ch-is-a-covalently-bonded-19b3561d) · Published by Druglandscape Ltd.