Properties of ionic compounds
AQA·Chemistry (Combined Science)·5.2.2.3·Trilogy — Higher
Notes for this section are being prepared.
Melting, boiling and electrical conductivity of ionic compounds
An ionic compound contains positive and negative ions arranged in a regular structure called an ionic lattice. Strong electrostatic attractions between oppositely charged ions hold the lattice together.
Melting and boiling points
To melt or boil an ionic compound, energy must be supplied to overcome the attractions between its ions. These attractions are strong, so a large amount of energy is needed. Ionic compounds therefore generally have high melting and boiling points.
Electrical conductivity
Electrical conduction requires charged particles that can move and carry charge through a substance. Ionic compounds contain charged ions, but whether they conduct depends on whether those ions are free to move.
- Solid: The ions are fixed in position in the lattice. They cannot carry charge through the solid, so it conducts poorly.
- Molten: The lattice has broken down and the ions can move. They carry charge through the liquid, so it conducts electricity.
- Dissolved in water: The ions separate and can move through the solution. They carry charge through the solution, so it conducts electricity.