Electron Pair Repulsion & Shape
- The valence shell electron pair repulsion theory (VSEPR) predicts the shape and bond angles of molecules
- Electrons are negatively charged and will repel other electrons when close to each other
- In a molecule, the bonding pairs of electrons will repel other electrons around the central atom forcing the molecule to adopt a shape in which these repulsive forces are minimised
- When determining the shape and bond angles of a molecule, the following VSEPR rules should be considered:
- Valence shell electrons are those electrons that are found in the outer shell
- Electron pairs repel each other as they have the same charge
- Lone pair electrons repel each other more than bonded pairs
- Repulsion between multiple and single bonds is treated the same as for repulsion between single bonds
- Repulsion between pairs of double bonds are greater
- The most stable shape is adopted to minimize the repulsion forces
- Different types of electron pairs have different repulsive forces
- Lone pairs of electrons have a more concentrated electron charge cloud than bonding pairs of electrons
- The cloud charges are wider and closer to the central atom’s nucleus
- The order of repulsion is therefore: lone pair – lone pair > lone pair – bond pair > bond pair – bond pair
Different types of electron pairs have different repulsive forces