Can you explain the bond angle and shape of the molecule NH3?

In NH3, the nitrogen atom is bonded to three hydrogen atoms. By drawing the Lewis structure, the central nitrogen atom shows 3 covalent bonds to hydrogen and one lone pair. Valence Shell Electron Pair Repulsion theory suggests that the optimum bond angles would be 109.5 degrees. But as an electron pair takes up slightly more space, the bond angle is 107 degrees. This leads to a pyrimidal shape.