# Explain why the electrical conductivity of metals decreases as temperature increases, whilst the electrical conductivity of semiconductors increases as temperature increases.

> IB DP Chemistry Higher Level (2023 syllabus) — S2.3 The metallic model · Explain · 4 marks

## Mark scheme (4 marks)

1. Metals contain a lattice of positive ions (cations) surrounded by delocalised electrons that carry charge / act as charge carriers.
2. As temperature increases, the positive ions in the metallic lattice vibrate with greater amplitude, increasing the frequency/degree of collisions with delocalised electrons and impeding electron flow, so conductivity decreases.
3. In semiconductors, electrons are (covalently) bonded / localised at low temperatures and are not available as charge carriers, so conductivity is initially low.
4. As temperature increases, electrons in semiconductors gain sufficient thermal energy to be promoted / excited across the (small) band gap, increasing the number of charge carriers and therefore increasing conductivity.

## Key terms

- [semiconductor](https://www.gradenine.co.uk/glossary/semiconductor)
- [electrical conductivity](https://www.gradenine.co.uk/glossary/electrical-conductivity)

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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