Explain the concept of hybridisation in covalent bonding.

Hybridisation in covalent bonding is the mixing of atomic orbitals to form new hybrid orbitals for bonding.

In more detail, hybridisation is a concept in molecular chemistry that describes the combination of atomic orbitals within an atom to produce new orbitals, known as hybrid orbitals. These hybrid orbitals are suitable for the pairing of electrons to form covalent bonds. The process of hybridisation occurs when atoms are preparing to bond together.

The concept of hybridisation was introduced to explain the molecular structure when the valence bond theory failed to correctly predict them. For instance, in the case of methane (CH4), the carbon atom forms four bonds with four hydrogen atoms. According to the valence bond theory, carbon should form two different types of bonds, but in reality, all four bonds in methane are identical. This discrepancy led to the concept of hybridisation.

There are different types of hybridisation, such as sp, sp2, sp3, dsp3, and d2sp3, depending on the types of orbitals involved in the mixing process. For example, in an sp3 hybridisation (like in methane), one s orbital and three p orbitals in the valence shell of the carbon atom mix to form four equivalent sp3 hybrid orbitals. Each of these orbitals can form a bond with a hydrogen atom, resulting in a molecule with a tetrahedral shape.

The concept of hybridisation is crucial in understanding the shapes and properties of molecules. It helps explain why certain molecules have specific shapes, as the shape of a molecule is determined by the arrangement of the hybrid orbitals. For example, molecules with sp hybridisation are linear, sp2 hybridised molecules are trigonal planar, and sp3 hybridised molecules are tetrahedral.

In summary, hybridisation is a key concept in covalent bonding, providing a more accurate description of the electron distribution around atoms when they form covalent bonds. It is a fundamental concept in understanding the structure and properties of molecules.