Sodium Chloride is an alkali halide with an fcc crystal structure. The basis is two ions, a sodium cation and a chlorine anion. The crystal lattice parameter is 0.563 nm. The diagram shows both a unit ...

Since the stoichiometry of the salt is 2:1, we must fill all of the tetrahedral holes (the FCC structure gives four selenides, thus we need eight lithiums). will occupy the latice points that define ...