Giant Ionic Lattices and Properties — AQA GCSE Chemistry
Ionic compounds form giant lattices, and this structure explains all their key properties.
The giant ionic lattice
In an ionic compound, the positive and negative ions are arranged in a regular, repeating 3D pattern called a giant ionic lattice. The ions are held together by strong electrostatic forces of attraction acting in all directions between oppositely charged ions.
A diagram of a lattice (e.g. sodium chloride) shows only a small part of a structure containing a very large number of ions.
Properties explained
| Property | Explanation |
|---|---|
| High melting/boiling points | many strong electrostatic forces need a lot of energy to break |
| Conduct when molten or dissolved | the ions become free to move and carry charge |
| Do not conduct when solid | the ions are fixed in position and cannot move |
| Often brittle | distorting the lattice brings like charges together, which repel |
Why state matters for conductivity
- Solid ionic compound → ions held in fixed positions → no conduction.
- Molten or dissolved → ions free to move → conducts electricity.
Exam tips
- Describe the structure as a giant ionic lattice with electrostatic forces in all directions.
- Explain the high melting point (many strong bonds).
- Explain conductivity in terms of free-moving ions (molten/dissolved only).
- A lattice diagram shows only a small repeating part of the structure.