Question:medium

Which of the following molecules contains maximum number of electrons in antibonding molecular orbitals?

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Antibonding electrons increase as you move from $\text{N}_2 \to \text{O}_2 \to \text{F}_2$ in the second period.
Updated On: May 7, 2026
  • $\text{Li}_2$
  • $\text{N}_2$
  • $\text{O}_2$
  • $\text{F}_2$
Show Solution

The Correct Option is D

Solution and Explanation

Step 1: Understanding the Concept:
Molecular Orbital Theory (MOT) dictates that electrons fill bonding and antibonding orbitals based on energy. Antibonding orbitals are marked with a star (\(\sigma^*\) or \(\pi^*\)).
Step 2: Key Formula or Approach:
Write the electronic configuration for each molecule and count electrons in starred (\(*\)) orbitals.
Step 3: Detailed Explanation:
(A) \(\text{Li}_2\) (6 electrons): \(\sigma_{1s}^2 \sigma_{1s}^{*2} \sigma_{2s}^2\). Total antibonding electrons = 2.
(B) \(\text{N}_2\) (14 electrons): \(\sigma_{1s}^2 \sigma_{1s}^{*2} \sigma_{2s}^2 \sigma_{2s}^{*2} \pi_{2p_x}^2 \pi_{2p_y}^2 \sigma_{2p_z}^2\). Total antibonding electrons = 4.
(C) \(\text{O}_2\) (16 electrons): \(\dots \sigma_{2p_z}^2 \pi_{2p_x}^2 \pi_{2p_y}^2 \pi_{2p_x}^{*1} \pi_{2p_y}^{*1}\). Total antibonding electrons = \(4 + 2 = 6\).
(D) \(\text{F}_2\) (18 electrons): \(\dots \sigma_{2p_z}^2 \pi_{2p_x}^2 \pi_{2p_y}^2 \pi_{2p_x}^{*2} \pi_{2p_y}^{*2}\). Total antibonding electrons = \(4 + 4 = 8\).
Step 4: Final Answer:
\(\text{F}_2\) has the maximum number of antibonding electrons (8).
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