Difference between Bonding and Antibonding Molecular Orbitals

Molecular Orbital Theory
Bonding Molecular Orbitals	Anti-Bonding Molecular Orbitals
Molecular orbitals formed by the additive effect of the atomic orbitals is called bonding molecular orbitals	Molecular orbitals formed by the subtractive effect of atomic is called anti-bonding molecular orbitals
Probability of finding the electrons is more in the case of bonding molecular orbitals	Probability of finding electrons is less in antibonding molecular orbitals. There is also a node between the anti-bonding molecular orbital between two nuclei where the electron density is zero.
These are formed by the combination of + and + and – with – part of the electron waves	These are formed by the overlap of + with – part.
The electron density, in the bonding molecular orbital in the internuclear region, is high. As a result, the nuclei are shielded from each other and hence the repulsion is very less.	The electron density in the antibonding molecular orbital in the internuclear region is very low and so the nuclei are directly exposed to each other. Therefore the nuclei are less shielded from each other.
The bonding molecular orbitals are represented by σ, π, δ.	The corresponding anti-bonding molecular orbitals are represented by σ∗ , π∗, δ∗.

The lowering of the energy of bonding molecular orbital than the combining atomic orbital is called stabilization energy and similarly increase in energy of the anti-bonding molecular orbitals is called destabilization energy.

Try this: Paramagnetic materials, those with unpaired electrons, are attracted by magnetic fields whereas diamagnetic materials, those with no unpaired electrons, are weakly repelled by such fields. By constructing a molecular orbital picture for each of the following molecules, determine whether it is paramagnetic or diamagnetic.

B₂
C₂
O₂
NO
CO

Features of Molecular Orbital Theory

The atomic orbitals overlap to form new orbitals called molecular orbitals. When two atomic orbitals overlap they lose their identity and form new orbitals called molecular orbitals.
The electrons in the molecules are filled in the new energy states called the Molecular orbitals similar to the electrons in an atom being filled in an energy state called atomic orbitals.
The probability of finding the electronic distribution in a molecule around its group of nuclei is given by the molecular orbital.
The two combining atomic orbitals should possess energies of comparable value and similar orientation. For example, 1s can combine with 1s and not with 2s.
The number of molecular orbitals formed is equal to the number of atomic orbitals combining.
The shape of molecular orbitals formed depends upon the shape of the combining atomic orbitals.

According to the Molecular Orbital Theory, the filling of orbitals takes place according to the following rules:

Aufbau’s principle: Molecular orbitals are filled in the increasing order of energy levels.
Pauli’s exclusion principle: In an atom or a molecule, no two electrons can have the same set of four quantum numbers.
Hund’s rule of maximum multiplicity: Pairing of electrons doesn’t take place until all the atomic or molecular orbitals are singly occupied.