In most simple ionic solids, the anions pack as efficiently as possible and the cations occupy spaces in the array of anions. The ions pack as closely as possible in most ionic solids. Four features are common to the packing observed in most ionic solids, even though the sizes of the ions vary widely.

Ions pack such that:
1. Ions of opposite charge touch so that the forces of attraction between these ions are as large as possible.

2. Each positive ion touches as many negative ions as possible in order to maximize the forces of attraction.

3. Positive ions do not touch other positive ions because they are small and strongly repel each other.

4. Negative ions can approach each other closely. In some structures, negative ions touch other negative ions.