Electron Pair Repulsion in Molecules

In molecules, the electron pairs around the central atom repel each other. This repulsion influences the molecular geometry, as the electron pairs try to arrange themselves as far apart as possible to minimize this repulsion. The Valence Shell Electron Pair Repulsion (VSEPR) theory explains this phenomenon.

Types of Electron Pairs and Repulsion Strength

There are generally two types of electron pairs around a central atom:

• Bond pairs: Electrons shared between two atoms, forming a covalent bond.
• Lone pairs: Valence electrons that are not involved in bonding and belong solely to the central atom.

Lone pairs occupy more space than bond pairs because they are only attracted by one nucleus (the central atom), while bond pairs are attracted by two nuclei (the central atom and the bonded atom). This difference in spatial distribution leads to varying degrees of repulsion between different types of electron pairs.

The strength of repulsion follows a specific order:

• Lone pair – Lone pair (lp-lp) repulsion
• Lone pair – Bond pair (lp-bp) repulsion
• Bond pair – Bond pair (bp-bp) repulsion

Comparing the strengths, lone pair – lone pair repulsion is the strongest, followed by lone pair – bond pair repulsion, and bond pair – bond pair repulsion is the weakest.

Therefore, the maximum repulsion occurs between two lone pairs.