On electrostatic grounds, each ion in solid sodium chloride is surrounded by 6 ions of the opposite charge.
In NaCl,Cl−forms ccp lattice, in which it is present on every corner and face centers. Na+are present at octahedral voids.
The vertices of a typical tetrahedron house the surrounding ions. The larger chloride ions are placed in a cubic array, while the smaller sodium ions fill all the cubic gaps (tetrahedral voids) between them in the terminology of close packing.
The halide or rock salt crystal structure is a frequent name for this basic structure, which can be seen in a variety of different compounds. It can be represented as a two atom basis face-centered cubic (FCC) lattice or two interpenetrating face-centered cubic lattice.