Question

H\(_2\) molecule is more stable than Li\(_2\) molecule, because:

• A. In H\(_2\) molecule \(\sigma_{1s}\) molecular orbitals are shielded by electrons.
• B. In H\(_2\) bond order is one.
• C. In Li\(_2\) molecule \(\sigma_{1s}\) molecular orbitals are shielded by electrons.
• D. In Li\(_2\) molecule outer \(\sigma_{2s}\) molecular orbitals are shielded by the inner electrons.

Hint:

In molecules like Li\(_2\), the shielding of outer electrons by inner electrons reduces the bond strength and stability of the molecule.

Answer 1

The Correct Option is D

Step 1: Understanding Stability of Molecules.
The stability of a molecule is related to its bond order, which is the difference between the number of electrons in bonding molecular orbitals and antibonding molecular orbitals. In H\(_2\), the bond order is one, and the molecular orbitals are not significantly shielded. In Li\(_2\), however, the \(\sigma_{2s}\) molecular orbitals are shielded by the inner electrons, which reduces the bonding interaction and makes the molecule less stable.

Step 2: Analyzing the options.
(A) In H\(_2\) molecule \(\sigma_{1s}\) molecular orbitals are shielded by electrons: Incorrect. This statement is not relevant for the stability comparison of H\(_2\) and Li\(_2\).
(B) In H\(_2\) bond order is one: Incorrect. This is true, but it does not explain why H\(_2\) is more stable than Li\(_2\).
(C) In Li\(_2\) molecule \(\sigma_{1s}\) molecular orbitals are shielded by electrons: Incorrect. This statement is not the reason for the instability of Li\(_2\).
(D) In Li\(_2\) molecule outer \(\sigma_{2s}\) molecular orbitals are shielded by the inner electrons: Correct. This shielding reduces the effective bonding and makes Li\(_2\) less stable than H\(_2\).

Step 3: Conclusion.
The correct answer is (D), as it explains the reduced stability of the Li\(_2\) molecule due to electron shielding.