Question

According to molecular orbital theory which of the following is correct.

• A. LUMO level of $C_2$ molecule is a $\sigma 2p_z$ orbital
• B. In $C_2$ molecule, both the bonds are $\pi$ - bonds
• C. In $C_2^{2-}$ ion, there are one $\sigma$ and two $\pi$ bonds
• D. All the above are correct

Answer 1

The correct option is D All the above are correct

(a) For $C_2$ molecule, the electronic configuration is:
$\sigma 1s^2{\sigma }^{\ast }1s^2\sigma 2s^2{\sigma }^{\ast }2s^2\pi 2p_x^2\pi 2p_y^2\sigma 2p_z^0$
Hence, lowest unoccupied molecular orbital is $\sigma 2p_z$ orbital.
(b) Double bond in $C_2$ consists of both $\pi$ bonds because of the presence of four electrons in 2 $\pi$ MO's.
(c) $C_2^{2-}$ ion has one $\sigma$ and two $\pi$ bonds.