Lone Pair-Lone Pair Repulsion

Lone pairs of electrons are the pairs of electrons that are not involved in any chemical bond. They are also known as non-bonding pairs or unshared pairs. The repulsion between lone pairs of electrons is stronger than the repulsion between bond pairs of electrons. This can be explained by the following factors:

1. Shape of Orbitals:
Lone pairs of electrons occupy more space around the central atom compared to bond pairs. This is due to the shape of the orbitals involved. Lone pairs are localized in specific orbitals, such as the s or p orbitals, while bond pairs are spread out over multiple orbitals. The greater spatial extent of lone pairs increases their repulsion with other electron pairs.

2. Electron Density:
Lone pairs have higher electron density compared to bond pairs. This is because lone pairs are attracted to the positive nucleus of the central atom and are not shared with any other atom. The higher electron density in lone pairs leads to stronger repulsion between them.

3. Distribution of Charge:
Lone pairs have a greater negative charge compared to bond pairs. This is because lone pairs are closer to the central atom and experience less shielding from other electrons. The greater negative charge in lone pairs results in stronger repulsion between them.

4. Electronegativity:
The electronegativity of the central atom also plays a role in lone pair-lone pair repulsion. Higher electronegativity of the central atom leads to stronger repulsion between lone pairs. This is because a more electronegative atom attracts electrons more strongly, causing the lone pairs to repel each other more.

Overall Effect:
Due to these factors, the lone pair-lone pair repulsion is greater than the bond pair-bond pair repulsion. This can affect the geometry of molecules and the angles between the bonded atoms. In some cases, the lone pair-lone pair repulsion may distort the bond angles and result in a non-linear molecular shape.

Conclusion:
Understanding the repulsion between lone pairs and bond pairs is crucial in predicting the geometry and properties of molecules. The stronger repulsion between lone pairs compared to bond pairs is due to factors such as the shape of orbitals, electron density, distribution of charge, and electronegativity of the central atom.