Chemistry - CHEMICAL BONDING Question with Solution | TestHub

Question Explanation: Identifying the diatomic molecule with exclusively $\pi$-bonding and finding its first empty molecular orbital.

Concept: Molecular orbital electronic configurations.

Solution: For C₂ (12 electrons), the molecular orbital configuration is:

${\sigma }_{1s}^2$, ${\sigma }_{1s}^{\ast 2}$, ${\sigma }_{2s}^2$, ${\sigma }_{2s}^{\ast 2}$, ${\pi }_{2px}^2={\pi }_{2py}^2$

* Since the last four electrons occupy only $\pi$ bonding orbitals, C₂ has two $\pi$-bonds and no $\sigma$-bond in its valence shell.

* The Highest Occupied Molecular Orbital (HOMO) consists of the ${\pi }_{2p}$ orbitals.

* The Lowest Unoccupied Molecular Orbital (LUMO) is the next orbital in the energy sequence, which is the ${\sigma }_{2pz}$ bonding orbital.

* Diagram (1) represents a $\sigma$-bonding orbital formed by head-on overlap.

Final Answer: Option (A)