Sodium chloride crystal, molecular model. Sodium chloride is common table salt. It comprises a regular arrangement of sodium (green) and chlorine (blue) ions. The ions of each form a cube, with another ion at the centre of each face of a cube, a configuration called face centred cubic. The ions of the other element fit in the gaps along each side of the cube. This leads to a system called cubic close packed, or the halite structure, after another name for the salt. The unit cell of the crystal, the part that is repeated throughout the structure, is outlined in red.