Which factor causes the slight deviation of bond angles from the idealized VSEPR angles in real molecules like chloromethane?

Answer

The electronegativity of the surrounding atoms

While the primary geometry is determined by domain count, differences in the surrounding atoms' electronegativity alter the electron density distribution, subtly changing the effective size and repulsion of specific bonds, thus slightly adjusting the bond angles.

Which factor causes the slight deviation of bond angles from the idealized VSEPR angles in real molecules like chloromethane?
electronAtomGeometrymoleculebond