JEE Main · 2024 · 29 Jan 2024 · Shift 2 · Chemical Bonding and Molecular Structure

In a homonuclear diatomic molecule, atomic orbitals combine to give molecular orbitals, and every bonding MO formed has a corresponding antibonding MO.

From the two 2s orbitals: ${\sigma }_{2s}$ (bonding) and ${\sigma }_{2s}^{\ast }$ (antibonding) — 1 antibonding MO.

From the three 2p orbitals on each atom: the pair lying along the internuclear axis gives ${\sigma }_{2p_z}$ and ${\sigma }_{2p_z}^{\ast }$; the two perpendicular pairs give ${\pi }_{2p_x},{\pi }_{2p_y}$ (bonding) and ${\pi }_{2p_x}^{\ast },{\pi }_{2p_y}^{\ast }$ (antibonding) — 3 antibonding MOs from 2p.

The total number of antibonding molecular orbitals formed from 2s and 2p orbitals is $1+3=4$.