Question

The correct order of energy levels of the molecular orbitals of N₂ is

• A. 1σ_g<1σ_u<2σ_g<2σ_u<1π_u<3σ_g<1π_g<3σ_u
• B. 1σ_g<1σ_u<2σ_g<2σ_u<3σ_u<3σ_u<1π_u<1π_g
• C. 1σ_g<1σ_u<2σ_g<2σ_u<1π_g<3σ_g<1π_u<3σ_u
• D. 1σ_g<1σ_u<2σ_g<2σ_u<3σ_g<1π_u<1π_g<3σ_u

Answer 1

The Correct Option is A

The molecular orbital configuration of nitrogen molecule (N₂) can be determined using the principles of molecular orbital theory. The energy levels of molecular orbitals are essential to understand how electrons are distributed within a molecule, which further explains the chemical bonding and properties of the molecule. 

For diatomic molecules, particularly those of homonuclear diatomic molecules like N₂, the energy order of molecular orbitals slightly varies as we move from lighter to heavier elements across the second period of the periodic table.

For N₂ (which has a total of 14 electrons), the correct energy level order of the molecular orbitals for the ground state configuration of N₂ is as follows:

1. 1σ_g - The lowest energy molecular orbital formed by the combination of 1s atomic orbitals.
2. 1σ_u - The next higher energy level due to antibonding interaction of 1s atomic orbitals.
3. 2σ_g - Formed by the combination of 2s atomic orbitals.
4. 2σ_u - Antibonding molecular orbital formed from 2s atomic orbitals.
5. 1π_u - Degenerate molecular orbitals formed by the side-on overlap of 2p orbitals, has lower energy compared to 3σ_g for N₂.
6. 3σ_g - Formed by the head-on overlap of 2p_z orbitals.
7. 1π_g - Antibonding orbitals formed from the 2p orbitals.
8. 3σ_u - The highest energy orbital (antibonding) of this sequence formed by 2p orbitals.

Therefore, the correct order of energy levels is:

1σ_g<1σ_u<2σ_g<2σ_u<1π_u<3σ_g<1π_g<3σ_u

This sequence explains why N₂ has a triple bond, leading to its high bond energy and stability.

Ruling out other options requires understanding of the switch in the order of \(1π_{\text{u}}\) and \(3σ_{\text{g}}\) after going past N₂, as the molecular orbital order differs for O₂ and beyond.