The differences in interactions between lone pairs and bonding pairs stem from their respective spatial distributions and repulsive effects.
Lone Pair-Lone Pair Interactions: Lone pairs are electrons that are not shared between atoms and are localized on a single atom. Since they occupy more space compared to bonding pairs, their interactions tend to be stronger due to greater electron-electron repulsion in a larger volume. When two lone pairs are near each other, the repulsive force is heightened since both are negatively charged and have more space to influence one another.
Lone Pair-Bonding Pair Interactions: When a lone pair interacts with a bonding pair, the interaction is moderate. The bonding pair consists of two electrons that are shared between atoms, which means there is a degree of overlap offered by the bonding that can shield the bonding electrons from the full repulsiveness of the lone pair’s charge. Thus, the interaction is weaker than that of two lone pairs.
Bonding Pair-Bonding Pair Interactions: In contrast, bonding pair interactions are generally the weakest among the three types. When two bonding pairs come close to each other, they experience some repulsion due to their shared nature, but the mutual attraction between the nuclei of the bonded atoms keeps them more stable and less repulsive compared to lone pair interactions.
In summary, the order of interactions can be understood as follows: lone pair-lone pair interactions are the strongest due to the extensive electron spread and repulsion, followed by lone pair-bonding pair interactions, and finally bonding pair-bonding pair interactions, which are the weakest. This hierarchy plays a crucial role in the geometry and reactivity of molecules, influencing their shapes and properties.