Explain why metals generally have high electrical conductivity and why this conductivity decreases as temperature increases.

IB DP Chemistry Standard Level (2023 syllabus) — S2.3 The metallic model · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Metals contain a lattice of positive ions surrounded by delocalised electrons.
These delocalised electrons can move freely through the lattice and carry charge, giving rise to electrical conductivity.
As temperature increases, the positive ions vibrate with greater amplitude.
Increased ionic vibration causes more frequent collisions and greater resistance to the flow of delocalised electrons, reducing conductivity.

Examiner tips

Use the exact terminology: "lattice of positive ions" and "delocalised electrons". Explain the mechanism in two parts: free electron movement and increased collisions. Show the cause–effect link between temperature and ion vibration.
Mention that conductivity decreases because resistance increases, not because electrons are lost.

Common mistakes

Confusing electrons with ions as the vibrating species. Using vague terms like "more heat" instead of "greater amplitude of vibration". Omitting the link between collisions and reduced conductivity.

Mark scheme (4 marks)

Metals contain a lattice of positive ions (cations) surrounded by delocalised electrons.
These delocalised electrons can move freely through the lattice and carry charge, giving rise to electrical conductivity.
As temperature increases, the positive ions vibrate with greater amplitude/more vigorously.
Increased ionic vibration causes more frequent collisions/greater resistance to the flow of delocalised electrons, reducing conductivity.

Key terms in this question

electrical conductivity