Definition of Molecular Orbital Theory
The bonding in terms of molecular orbitals, in which the orbitals are associated with the whole molecule and not individual atoms, is described by Molecular Orbital Theory. The molecules usually involve some kind of resonance which describes that the bond is a hybrid of both single as well as a double bond. So, the explanation for resonance bonding is described by MOT.
There are some principles of MOT. The first principle states that the number of molecular orbitals is the same as the number of atomic orbitals that have formed them. Second explains that the energy of bonding orbitals is lower than that of the atomic orbitals which have formed them. Whereas, antibonding orbitals have energy higher than that of the atomic orbitals which have formed them. The third one states that electrons present in the molecule are being assigned to orbitals from the lower or higher energy and the fourth principle states the molecular orbitals are most effectively formed when the atomic orbitals have the same energy.