Question

Comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option.

Molecular orbitals are formed by the overlap of atomic orbitals. Two atomic orbitals combine to form two molecular orbitals called bonding molecular orbital (BMO) and anti-bonding molecular orbital (ABMO). Energy of anti-bonding orbital is raised above the parent atomic orbitals that have combined and the energy of the bonding orbital is lowered than the parent atomic orbitals.

Energies of various molecular orbitals for elements hydrogen to nitrogen increase in the order :

$\sigma 1s<{\sigma }^{\ast }1s<\sigma 2s<{\sigma }^{\ast }2s<(\pi 2p_x\approx \pi 2p_y)<\sigma 2p_z<({\pi }^{\ast }2p_x\approx {\pi }^{\ast }2p_y)<{\sigma }^{\ast }2p_z$ and for oxygen and fluorine order of energy of molecular orbitals is given below :
$\sigma 1s<{\sigma }^{\ast }1s<\sigma 2s<{\sigma }^{\ast }2s<\sigma 2p_z<(\pi 2p_x\approx \pi 2p_y)<({\pi }^{\ast }2p_x\approx {\pi }^{\ast }2p_y)<{\sigma }^{\ast }2p_z$
Different atomic orbitals of one atom combine with those atomic orbitals of the second atom which have comparable energies and proper orientation. Further, if the overlapping is head on, the molecular orbital is called 'Sigma', $\left(\sigma \right)$ and if the overlap is lateral, the molecular orbital is called 'pi', $\left(\pi \right)$. The molecular orbitals are filled with electrons according to the same rules as followed for filling of atomic orbitals. However, the order for filling is not the same for all molecules or their ions. Bond order is one of the most important parameters to compare the strength of bonds.

• A. In the formation of dioxygen from oxygen atoms 10 molecular orbitals will be formed.
• B. Total number of bonding molecular orbitals will not be same as total number of anti bonding orbitals in dioxygen
• C. All the molecular orbitals in the dioxygen will be completely filled
• D. Number of filled bonding orbitals will be same as number of filledanti-bonding orbitals.

Answer 1

The correct option is A

In the formation of dioxygen from oxygen atoms 10 molecular orbitals will be formed.

Molecular orbital diagram of $O_2$ molecule

Experimental energy order of molecular orbitals:
$\sigma 1s<{\sigma }^{\ast }<\sigma 2s<{\sigma }^{\ast }2s<\sigma 2p_z<(\pi 2p_x=\pi 2p_y)<({\pi }^{\ast }2p_x={\pi }^{\ast }2p_y)<{\sigma }^{\ast }2p_x$

Molecular orbital diagram of $O_2$:




Analysing the options

Option (A)

From the molecular orbital diagram, the total number of molecular orbitals formed is 10. So, option (A) is correct.

Option (B)

From the molecular orbital diagram, two molecular orbitals in the dioxygen are partially filled and one molecular orbital is empty. So, option (B) is incorrect.


Option (C)

From the molecular orbital diagram, total number of bonding molecular orbitals is same as the total number of anti-bonding molecular orbitals in dioxygen. So, option (C) is incorrect.

Option (D)

From the molecular orbital diagram, number of filled bonding orbitals is not the same as the number of filled anti-bonding orbitals. So, option (D) is incorrect.

Hence, option (A) is correct.