In this Letter, we propose a semi-empirical procedure through which the charge factors, appearing in the simple overlap model (SOM) for the ligand field in lanthanide compounds, can be obtained. The idea is based on the concept of bond valence and bond strength introduced by Pauling in the 1920's. The charge factors thus obtained are used in the calculation of the so-called ligand held parameters, B-q(k)'s, and, subsequently, in the prediction of the Stark levels of the F-7(J) manifolds (J = 1,2, 3 and 4) of the Eu3+ ion in coordination compounds with mixed ligands. Comparison with experiment shows that the results are quite satisfactory.