In order to find an explanation for the WALSH rules on a more theoretical basis for molecules of type AB2 (non hydrides) a simple MO-LCAO calculation with SLATER-Functions of the L-shell was carried out. The results are presented as tables and graphs, which give the dependence of the one-electron energies on the valence angle. In accordance with WALSH’S rules the apex angle decreases with the number of electrons in the range of 16 to 20 valency electrons, molecules with not more than 16 valency electrons being linear. However according to the present calculation the reason for this is that with increasing number of electrons more orbitals are occupied which are lower in energy for the bent species, rather than WALSH’S explanation which lies in the increasing s-character of the πU non-bonding orbital.