# Explain why silicon dioxide (SiO₂) has a much higher melting point than carbon dioxide (CO₂), despite both compounds having the same empirical formula type.

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

## Mark scheme (4 marks)

1. CO₂ is a simple molecular substance / consists of discrete CO₂ molecules
2. CO₂ molecules are held together only by weak London/van der Waals dispersion forces, which require little energy to overcome
3. SiO₂ has a giant covalent / macromolecular / network covalent structure in which each Si atom is covalently bonded to four O atoms (and each O to two Si atoms) throughout the entire lattice
4. Melting SiO₂ requires breaking many strong covalent bonds throughout the entire network, requiring a very large amount of energy

## Key terms

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

## Related

- [Revision notes for IB DP Chemistry Standard 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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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-silicon-dioxide-sio-has-caa5af0d) · Published by Druglandscape Ltd.