Crystal structure of NaCl.
The salient features of its structure are:
Chloride ions are ccp type of arrangement, i.e., it contains chloride ions at the corners and at the center of each face of the cube.
Sodium ions are so located that there are six chloride ions around it. This equivalent to saying that sodium ions occupy all the octahedral sites.
As there is only one octahedral site for every chloride ion, the stoichiometry is 1 : 1.
It is obvious from the diagram that each chloride ion is surrounded by six sodium ions which are disposed towards the corners of a regular octahedron. We may say that cations and anions are present in equivalent positions and the structure has 6 : 6 coordination.
The structure of sodium chloride consists of eight ions a unit cell, four are Na+ ions and the other four are Cl– ions.
In this structure, each corner ion is shared between eight unit cells, each ion a face of the cell by two cells, each ion on a edge by four cells and the ion inside the cell belongs entirely to that unit cell.