Ion Mobility
Summary: The ability of ions to move freely through a substance or solution. Tags: igcse chemistry keyword Created: 2026-08-06
Ion mobility describes whether ions are free to move within a substance. In an ionic compound in the solid state, the ions are held in fixed positions in a giant ionic lattice by strong electrostatic forces, so they cannot move — they can only vibrate about their lattice positions. This is why solid ionic compounds do not conduct electricity.
When the compound is molten (heated above its melting point) or dissolved in water (aqueous), the lattice breaks down and the ions become free to move around. The key IGCSE exam point is that ionic compounds conduct electricity only when molten or aqueous, because in these states the ions are mobile and can carry charge — positive ions (cations) move towards the negative electrode and negative ions (anions) move towards the positive electrode. Conductivity is a direct test of ion mobility.
Sources
- Cambridge IGCSE Chemistry 0620 Syllabus (2023-2025), Cambridge Assessment International Education
Common Misconceptions
| Misconception | Reality |
|---|---|
| Solid ionic compounds conduct electricity | In the solid state ions are fixed in the lattice and cannot move, so the solid does not conduct |
| Ions are mobile in all states of matter | Ions are only mobile when molten or in aqueous solution; in the solid state they are held in fixed positions |
| Ion mobility means the ions leave the substance | Mobility means the ions move through the molten substance or solution, carrying charge from one electrode to the other |