In NaCl lattice structure, each Na⁺ ion has 12 Na⁺ ions as the next neighbour.

The NaCl structure can be considered as two interpenetrating FCC lattices. Each has 6 nearest neighbours of opposite charges, i.e, the co-ordination number is 6 (which is the number of nearest neighbours of an atom in a crystal).

Each Ca⁺ ion has 6 Cs⁺ ions as the next nearest neighbour at a distance of r = d_Cl-Cl-.

The CsCl is an ionic structure showing two interpenetrating simple cubic lattices, one for each kind of ion. It has a coordination number 8.