Question

The electronic configuration of carbon is $1s^2 2s^2 2p^2$. There are $12$ electrons in $C_2$. The correct electronic configuration of $C_2$ molecule is

• A. $\left(\sigma 1s^{2}\right)\left(\sigma^* 1s^{2}\right)\left(\sigma 2s^{2}\right)\left(\sigma^* 2s^{2}\right)\left(\sigma 2p_{z}^{2}\right)\left(\pi 2p_{x}^{2}\right)$
• B. $\left(\sigma 1s^{2}\right)\left(\sigma^* 1s^{2}\right)\left(\sigma 2s^{2}\right)\left(\sigma^* 2s^{2}\right)\left(\pi 2p_{x}^{2} = \pi2p_{y}^{2}\right)$
• C. $\left(\sigma 1s^{2}\right)\left(\sigma^* 1s^{2}\right)\left(\sigma 2s^{2}\right)\left(\sigma^* 2s^{2}\right)\left(\sigma 2p_{z}^{2}\right) \left(\pi 2p_{x}^{1} = \pi2p_{y}^{1}\right)$
• D. $\left(\sigma 1s^{2}\right)\left(\sigma^* 1s^{2}\right)\left(\sigma 2s^{2}\right)\left(\sigma^* 2s^{2}\right) \left(\pi 2p_{x}^{2} = \pi2p_{y}^{1}\right)$

Answer 1

Answer: (B)

$\left(\sigma 1s^{2}\right)\left(\sigma^* 1s^{2}\right)\left(\sigma 2s^{2}\right)\left(\sigma^* 2s^{2}\right)\left(\pi 2p_{x}^{2} = \pi2p_{y}^{2}\right)$

Answer 2

For atoms like nitrogen and below $N$ in atomic number have higher energy for $p_{z}$ -orbital, hence the configuration for $C_{2}$ molecule is $\left(\sigma 1s^{2}\right)\left(\sigma^* 1s^{2}\right)\left(\sigma 2s^{2}\right)\left(\sigma^* 2s^{2}\right) \left(\pi 2p_{x}^{2} = \pi2p_{y}^{2}\right)$.