# Explain why graphene is an excellent electrical conductor, whilst diamond is a poor electrical conductor, despite both being allotropes of carbon.

> IB DP Chemistry Higher Level (2023 syllabus) — S2.4 From models to materials · Explain · 4 marks

## Mark scheme (4 marks)

1. In graphene, each carbon atom forms three sigma bonds (sp2 hybridised), leaving one electron in an unhybridised p orbital per carbon atom.
2. These p electrons overlap laterally across the entire sheet to form a delocalised pi system / sea of delocalised electrons that are free to move and carry charge.
3. In diamond, each carbon atom forms four sigma bonds (sp3 hybridised) using all four valence electrons, leaving no electrons available for conduction.
4. Because diamond has no mobile charge carriers (no free electrons or ions), it cannot conduct electricity, whereas graphene's delocalised electrons act as mobile charge carriers, making it highly conductive.

## Key terms

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

## Related

- [Revision notes for IB DP Chemistry Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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