This paper discusses the calculation of internuclear distances by a soft-sphere ionic radii model for twenty crystalline Group 1 halides and hydrides and three ammonium halides with either sodium chloride or caesium chloride structures. It also describes calculation of internuclear distances with the soft-sphere model for three crystalline Group 2 fluorides with fluorite structures and fifteen Group 2 crystalline binary salts (oxides, sulfides, selenides and tellurides) with sodium chloride structures. Soft-sphere calculated radii for Group 1 salts are compared with other theoretical radii. Soft-sphere calculated results agree very well with experimental measurements in all cases except for lithium hydride. The probable reasons for the discrepancy with lithium hydride and merits of the soft sphere model are discussed. A simple expression to calculate lattice energies using the soft-sphere radii concept is given and results compared well with lattice energies calculated by the Born–Haber cycle.