Why do ionic compounds conduct electricity when molten but not when solid?
Ionic compounds conduct when molten or dissolved because the ions are then free to move and carry charge; in the solid the ions are locked in place.
GCSE Chemistry
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In more detail
Electricity is carried by moving charged particles. In a solid ionic lattice the ions are held in fixed positions by strong electrostatic forces, so they cannot move and the solid does not conduct. When the compound is melted (or dissolved in water), the lattice breaks apart and the ions become free to move towards the electrodes, carrying charge — so it conducts.
Key points for the exam
- Conduction needs charged particles that are free to move.
- Solid: ions fixed in the lattice → no conduction.
- Molten/dissolved: ions free to move → conducts.
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