# What can cause distortion in bond angles in VSEPR shapes?

Consider the water molecule...there are two bonding orbitals, i.e. the $O - H$ bonds, and two non-bonding lone pairs around the central oxygen atom. VESPER predicts that the electronic geometry should be tetrahedral... And in fact it is, and molecular shape is based on this geometry.
However, the oxygen-based lone pairs, are considered to lie close to the central oxygen...(i.e. as lone pairs they are not constrained to interact with ANOTHER atom). And the lone pairs are conceived to compress the $\angle H - O - H$ down from ${109.5}^{\circ}$ to the observed ${104.5}^{\circ}$.
Ammonia, $N {H}_{3}$, is another goto example...what are the $\angle H - N - H$ bond angles in this molecule? How do they compare with the bond angles in ammonium ion, $N {H}_{4}^{+}$?