Although the VSEPR model is correct in predicting that CH4 is tetrahedral, NH3 is pyramidal, and H2O is bent, the model in its simplest form does not account for the fact that these molecules do not have exactly the same bond angles (, HCH is 109.5 degrees, as expected for a tetrahedron, but, HNH is 107.3 degrees and , HOH is 104.5 degrees). Explain these deviations from the tetrahedral angle.