Q. Explain Valence Bond Theory?

This concept starts with the assumption that the bond between the metal ion and the ligand is basically covalent in nature. In order to form a chemical bond the central metal ion must have enough of vacant orbitals to accept the lone pairs of electrons from the ligands. The number of bonds formed is thus' directly related to the number of vacant orbitals on the metal ion. At this stage. Pauling introduced the concept of hybridised atomic orbitals.  Accordingly, the vacant atomic orbitals on the metal ion combine to give a set of hybridised orbitals. For hybridisation only those orbitals are used which have the correct orientation in space and whose energy values are very near to each other. These hybridised orbitals overlap with the ligand orbitals to share the lone pairs of electrons from the ligands. Since these hybridised orbitals show a definite orientation in space, the geometry of the molecule is determined by the kind of hybridisation involved.

In Table, the numbers shown in paranthesis represent the number of specific. Orbitals involved in hybridisation. They do not indicate either the principal quantum number or the number of electrons in a particular orbital.