What is the role of d-orbitals in molecular hybridisation?

D-orbitals play a crucial role in molecular hybridisation by expanding the valence shell to accommodate more electrons for bonding.

In more detail, molecular hybridisation is a concept in chemistry that explains the formation of chemical bonds in molecules. It involves the mixing of atomic orbitals to form new hybrid orbitals, which can accommodate more electrons and thus form more bonds. The d-orbitals come into play in this process, particularly in elements in the third period and beyond on the periodic table.

These elements have d-orbitals in their valence shell, which can be used for bonding. This is because as we move down the groups in the periodic table, the energy difference between the s, p and d orbitals decreases, making it possible for the d-orbitals to participate in hybridisation. This is known as d-orbital hybridisation, and it allows these elements to form more than the usual number of bonds. For example, phosphorus in PCl5 and sulphur in SF6.

The d-orbitals are particularly important in transition metals, which have partially filled d-orbitals. These d-orbitals can hybridise with the s and p orbitals to form hybrid orbitals, which can then form bonds. This is why transition metals often have high coordination numbers - they can form many bonds due to the availability of d-orbitals for hybridisation.

In summary, the role of d-orbitals in molecular hybridisation is to expand the valence shell of an atom, allowing it to accommodate more electrons for bonding. This is particularly important in elements in the third period and beyond, and in transition metals, where the d-orbitals can hybridise with the s and p orbitals to form more bonds.