Question

Which of the following diatomic molecular species has only bonds according to Molecular Orbital Theory?

• A. \(O_2\)
• B. \(N_2\)
• C. \(C_2\)
• D. \(B_2\)

Answer 1

The Correct Option is C

The question asks us to determine which diatomic molecular species has only π (pi) bonds according to Molecular Orbital (MO) Theory. Let's analyze each option:

1. O_2: According to MO theory, O_2 has the electronic configuration \sigma_{1s}^2\sigma^{*}_{1s}^2\sigma_{2s}^2\sigma^{*}_{2s}^2\sigma_{2p_z}^2\pi_{2p_x}^2\pi_{2p_y}^2\pi^{*}_{2p_x}^1\pi^{*}_{2p_y}^1. This means O_2 has both σ (sigma) and π bonds.
2. N_2: For N_2, the electronic configuration is \sigma_{1s}^2\sigma^{*}_{1s}^2\sigma_{2s}^2\sigma^{*}_{2s}^2\sigma_{2p_z}^2\pi_{2p_x}^2\pi_{2p_y}^2. This results in one σ and two π bonds, usually contributing to the stability of N_2 with a triple bond (one σ and two π).
3. C_2: For C_2, the electronic configuration is \sigma_{1s}^2\sigma^{*}_{1s}^2\sigma_{2s}^2\sigma^{*}_{2s}^2\pi_{2p_x}^2\pi_{2p_y}^2. Notably, there are no electrons in the \sigma_{2p_z} orbital. Thus, C_2 has only π bonds, making it unique among the given options.
4. B_2: The electronic configuration for B_2 is \sigma_{1s}^2\sigma^{*}_{1s}^2\sigma_{2s}^2\sigma^{*}_{2s}^2\pi_{2p_x}^1\pi_{2p_y}^1, involving one bond which includes both σ and π components.

In conclusion, the diatomic molecular species C_2 has only π bonds according to Molecular Orbital Theory. This is due to its unique electron configuration where all bonding electrons in the valence shell participate in π bonding without any σ bond involvement. Thus, the correct answer is C_2.