How does hybridisation affect bond angles in molecules?

Hybridisation affects bond angles in molecules by determining the spatial arrangement of the electron pairs around the central atom.

Hybridisation is a concept in molecular chemistry that describes the mixing of atomic orbitals to form new hybrid orbitals. These hybrid orbitals are used in the formation of chemical bonds. The type of hybridisation (sp, sp2, sp3, etc.) determines the geometry of the molecule and hence the bond angles.

For instance, in an sp hybridisation, there are two hybrid orbitals formed. These orbitals arrange themselves in a linear fashion to minimise electron repulsion, resulting in a bond angle of 180 degrees. This is seen in molecules like BeCl2.

In sp2 hybridisation, three hybrid orbitals are formed. They arrange themselves in a trigonal planar fashion, leading to bond angles of 120 degrees. This is observed in molecules like BF3.

In sp3 hybridisation, four hybrid orbitals are formed. They arrange themselves in a tetrahedral fashion, resulting in bond angles of 109.5 degrees. This is seen in molecules like CH4.

The concept of hybridisation is closely linked to Valence Shell Electron Pair Repulsion (VSEPR) theory. According to this theory, electron pairs around a central atom arrange themselves to minimise repulsion, which in turn determines the shape of the molecule and the bond angles. The type of hybridisation gives us a clue about the number of electron pairs around the central atom and hence the geometry of the molecule.

In summary, hybridisation plays a crucial role in determining the bond angles in molecules. By understanding the type of hybridisation, we can predict the geometry of the molecule and the bond angles. This is a fundamental concept in chemistry that helps us understand the structure and properties of molecules.