Orbital hybridisation is the concept of mixing atomic orbitals into new hybrid orbitals suitable for the pairing of electrons to form chemical bonds in valence bond theory.

Hybridization
Hybridization is a concept in chemistry that involves the mixing of atomic orbitals to form new hybrid orbitals. These hybrid orbitals are better suited for bonding compared to the original atomic orbitals.

Types of Hybridization
There are several types of hybridization, including:
- sp hybridization: formed by mixing one s orbital with one p orbital to create two sp hybrid orbitals.
- sp2 hybridization: formed by mixing one s orbital with two p orbitals to create three sp2 hybrid orbitals.
- sp3 hybridization: formed by mixing one s orbital with three p orbitals to create four sp3 hybrid orbitals.
- sp3d hybridization: formed by mixing one s orbital with three p orbitals and one d orbital to create five sp3d hybrid orbitals.
- sp3d2 hybridization: formed by mixing one s orbital with three p orbitals and two d orbitals to create six sp3d2 hybrid orbitals.

Importance of Hybridization
Hybridization allows atoms to form strong and stable bonds by maximizing electron density between atoms. It also helps in explaining the geometry and shape of molecules. For example, sp3 hybridization results in a tetrahedral geometry, while sp2 hybridization results in a trigonal planar geometry.

Applications of Hybridization
Hybridization is essential in understanding the reactivity and properties of molecules in organic chemistry. It is also used in molecular biology to study the structure and function of biological molecules.
In conclusion, hybridization plays a crucial role in shaping the molecular world and understanding the behavior of atoms in chemical reactions.