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 requires us to determine which diatomic molecular species have only pi bonds according to Molecular Orbital Theory. The options given are: \(O_2\), \(N_2\), \(C_2\), \(B_2\). Let's analyze each molecule based on Molecular Orbital Theory.

Molecular Orbital (MO) Configuration:

• \(O_2\): The electron configuration is \((\sigma_{2s})^2(\sigma^*_{2s})^2(\sigma_{2p_z})^2(\pi_{2p_x}=\pi_{2p_y})^4(\pi^*_{2p_x}=\pi^*_{2p_y})^2\). Here, there are both sigma and pi bonds.
• \(N_2\): The electron configuration is \((\sigma_{2s})^2(\sigma^*_{2s})^2(\pi_{2p_x}=\pi_{2p_y})^4(\sigma_{2p_z})^2\). This molecule consists of a strong triple bond (one sigma and two pi bonds).
• \(C_2\): The electron configuration is \((\sigma_{2s})^2(\sigma^*_{2s})^2(\pi_{2p_x}=\pi_{2p_y})^4\). There are only pi bonds according to its MO configuration, since the sigma bond from \sigma_{2p_z} is not populated.
• \(B_2\): The electron configuration is \((\sigma_{2s})^2(\sigma^*_{2s})^2(\pi_{2p_x}=\pi_{2p_y})^2\). It has only one pi bond.

Conclusion:

Among the given options, \(C_2\) is the only molecule that, according to Molecular Orbital Theory, has only pi bonds. It lacks a sigma bond in the \sigma_{2p_z} orbital, which is unoccupied.