The lattice energy of an ionic crystal, U-POT, can be expressed as a linear function of the inverse cube root of its formula unit volume (i.e., V-m(-1/3)); thus, U-POT 2/(alpha/V-m(1/3) + beta), where alpha and beta are fitted constants and I is the readily calculated ionic strength factor of the lattice. The standard entropy, S, is a linear function of V-m itself: S kV(m) + c, with fitted constants k and c. The constants a and beta have previously been evaluated for salts with charge ratios of 1:1, 1:2, and 2:1 and for the general case q:p, while values of k and c applicable to ionic solids generally have earlier been reported. In this paper, we obtain alpha and beta, k and c, specifically for 2:2 salts (by studying the ionic oxides, sulfates, and carbonates), finding that U-POT{MX 2:2}(kJ mol(-1)) approximate to 8(119/V-m(1/3) + 60) and S-o{MX 2:2}/(J K-1 mol(-1)) 1382V(m) + 16.