Question

Anti-bonding molecular orbital is formed by:
A.Addition of atomic orbitals
B.Subtraction of atomic orbitals
C.Multiplication of atomic orbitals
D.None of these

Answer 1

Molecular Orbital theory was developed to explain the bonding in molecules that cannot be explained by Valence Bond Theory. These molecules generally show resonance. Resonance means that a bond is a hybrid of the shared electrons.

Complete step by step answer:
Anti-bonding orbitals are formed where the atomic orbitals combine such that it leads to predominantly destructive interference i.e. subtraction of wave function. The most important feature of antibonding orbitals is that the molecular orbitals have higher energy than the corresponding atomic orbitals. Therefore, the molecule has higher energy than the isolated separate atoms.

Therefore, we can conclude that the correct answer to this question is option B.

Additional information:
Important characteristics of Bonding Molecular Orbitals
-The probability of finding the electron in the internuclear region of the bonding molecular orbital is more than that of combining atomic orbitals.
-The presence of electrons present in the bonding molecular orbital is the cause of attraction between the two atoms.
-The bonding molecular orbital has lower energy as a result of attraction and hence has greater stability than that of the combining atomic orbitals.
-They are formed by the additive effect of the atomic orbitals so that the amplitude of the new wave is given by $\Phi = \;{\Psi _A}\; + {\text{ }}{\Psi _B}$
-They are represented by $\sigma ,{\text{ }}\pi ,{\text{ and }}\delta$
Important characteristics of Anti-bonding Molecular Orbitals
-The probability of finding the electron in the internuclear region decreases in the antibonding molecular orbitals.
- The electrons present in the antibonding molecular orbital result in the repulsion between the two atoms.
-The anti-bonding molecular orbitals have higher energy because of the repulsive forces and lower stability.
They result from the subtractive effect of the atomic orbitals. The amplitude of the new wave is given by:
$\Phi = \;{\Psi _A}\; - {\text{ }}{\Psi _B}$
They are represented by ${\sigma ^ * },{\text{ }}{\pi ^ * },{\text{ }}{\delta ^ * }$

Note:
The filling of these orbitals takes place in the order of increasing energy and is governed by the following rules:
-The molecular orbitals are arranged in the increasing order of their energies. The molecular orbital with the lowest energy is filled first as per the Aufbau principle.
-Each molecular orbital can accommodate a maximum of two electrons with opposite spins as per Pauli's exclusion principle.
-If there are two or more molecular orbitals of the same energy, these are the first singly filled and then pairing starts as per the Hund's rule.