How do bonding pairs and lone pairs repel each other in VSEPR theory?

In VSEPR theory, molecular shape is determined by the principle that all electron pairs—both bonding pairs and lone pairs—repel one another to minimize their mutual interactions.12

The strength of these repulsive forces is not uniform. According to the theory, the magnitude of repulsion follows this order:2

• Lone pair–lone pair: Greatest repulsion.
• Lone pair–bonding pair: Intermediate repulsion.
• Bonding pair–bonding pair: Least repulsion.

This hierarchy is qualitatively explained by the idea that lone pairs are associated with only a single nucleus, allowing them to occupy a larger volume of space compared to bonding pairs, which are constrained between two attracting centers.2

Because of these varying repulsive strengths, molecules often exhibit bond angles that deviate from ideal geometric arrangements. For example, in water and ammonia, the presence of lone pairs causes bonding pairs to be pushed closer together, resulting in bond angles smaller than the ideal tetrahedral angle of 109.5°.2