* Electron Pair Repulsion: Lone pairs and bonding pairs of electrons around a central atom all repel each other. This repulsion is based on the principle of minimizing electron-electron interactions.
* Lone Pairs vs. Bonding Pairs: Lone pairs are localized on the central atom, while bonding pairs are shared between two atoms. This difference in electron distribution makes lone pairs exert a stronger repulsive force than bonding pairs.
* Resulting Bond Angle Changes: The stronger repulsion from lone pairs causes the bonding pairs to be pushed closer together, resulting in a smaller bond angle than expected from the ideal geometry based solely on bonding pairs.
Example:
* Water (H2O): Oxygen has two lone pairs and two bonding pairs. The ideal geometry would be tetrahedral with bond angles of 109.5°. However, the lone pairs push the bonding pairs closer together, resulting in a bond angle of 104.5°.
Generalizations:
* More lone pairs = smaller bond angles: The more lone pairs an atom has, the smaller the bond angles will be.
* Lone pair-bond pair repulsion > bond pair-bond pair repulsion: The repulsion between a lone pair and a bonding pair is stronger than the repulsion between two bonding pairs.
Important Note:
While lone pairs influence bond angles, other factors like the size of the central atom and the electronegativity of the surrounding atoms also play a role.
Understanding how lone pairs affect bond angles is crucial for predicting the shapes of molecules and their chemical properties.
