Molecular Orbital calculations on 31 H3:e_mxm+N:e hydronitride molecules containing 3-, 4-, and 6-coordinate X-cations from rows 1-4 of the periodic table yield minimum energy bond lengths, Rt(XN), which reproduce observed bond lengths, Ro(XN), in crystalline nitrides to within o.O₃A, on average. A linear regression analysis of In[Rt(XN)] vs. In(p) with p = air, where a is the Pauling bond strength and r is the row number of the X -cation in the periodic table, gives the equation R(XN) = 1.47p-O.2\ which is shown to reproduce the observed XN bond lengths of Baur (1987) to within o.o9A, on average. This equation is statistically identical to the equation R( XN) 1.49p-O.22, derived from a linear regression analysis ofln[Ro{XN)] vs. In(p), and is similar in form to those obtained for the oxides (R(XO) = 1.39p-O.22) and the sulfides (R(XS) = 1.83p-O.21).