# Explain why the electrical conductivity of silicon increases as temperature increases, whereas the electrical conductivity of copper decreases as temperature increases.

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

## Mark scheme (4 marks)

1. Silicon is a semiconductor; at low temperatures there are few charge carriers / electrons in the conduction band.
2. As temperature increases, more electrons gain sufficient thermal energy to cross the band gap into the conduction band, increasing the number of charge carriers and thus conductivity.
3. Copper is a metallic conductor with a partially filled conduction band / large number of delocalised electrons already available as charge carriers.
4. As temperature increases, greater thermal vibration of the copper lattice ions increases resistance / impedes electron flow, so conductivity decreases.

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