Question

Explain the postulates of molecular orbital theory.

Answer 1

Hint: Molecular orbital theory is also represented by (MOT); it is a method used for describing the electronic structure of various molecules. According to this theory, electrons are treated as moving under the influence of the nuclei in the whole molecule.

Complete answer:
The Valence Bond Theory fails to account for energies of different structures, and doesn’t account for the detailed magnetic properties beyond telling the number of unpaired electrons. We will be mentioning molecular orbital theory as MOT from now on ward in the answer. That’s why MOT can explain the answer to these questions. There are various postulates of MOT found like:
> According to the Molecular Orbital Theory, it is also found that individual atoms combine to form molecular orbitals. Therefore, we can see that the electrons of an atom are present in various atomic orbitals.
> It is found that MOT considers that an electron in a molecule moves in a field of more than one nucleus and one or more than one electrons. Thus the molecular orbitals are polycentric.
> Just as there are atomic orbitals s, p, d, f in an atom. There are molecular orbitals \[\sigma ,\pi ,\delta \] in a molecule.
> There are two molecular orbitals present, that is bonding molecular orbital and antibonding molecular orbital.
> The energy of bonding molecular orbital (BMO) and antibonding molecular orbital (ABMO) is found as:
It is found that the energy of BMO is less than that of ABMO. This is because of the increase in the attraction of both the nuclei for both the electron (of the combining atom).
Energy of ABMO is found to be higher than that of BMO. This is because the electron tries to move away from the nuclei and is in a repulsive state.
> We have to follow certain rules while filling up molecular orbitals with electrons in order to write correct molecular configurations. They are:
- Aufbau Principle – This principle states that those molecular orbitals which have the lowest energy are filled first.
- Pauli’s Exclusion Principle – According to this principle, each molecular orbital can accommodate a maximum of two electrons having opposite spins.

Note: It is important to note here that the valence electrons are considered to be associated with all the nuclei in the molecule. Thus the atomic orbitals must be combined to produce molecular orbitals. The magnetic properties are very well defined in MOT.