Question

Which of the following molecules exist?

• A. $He_2$
• B. $Be_2$
• C. $Ne_2$
• D. $C_2$

Answer 1

The Correct Option is D

$He_{2} : \sigma1s^{2}, \sigma^* 1s^{2}$
B.O. = $ \frac{1}{2} (2 -2) = 0 , He_2$ does not exist.
$Be_2 :\sigma 1s^{2}, \sigma^* 1s^{2} ,\sigma^* 2s^{2} $
B.O. $ = \frac{1}{2}(4 - 4) = 0, Be_2$ does not exist.
$ Ne_{2} =\sigma 1s^{2}, \sigma^* 1s^{2},\sigma 2s^{2},\sigma^* 2s^{2}, \sigma 2p^{2}_{z} ,\left(\pi2p_{x}^{2} =\pi2p_{y}^{2}\right)\left(\pi^* 2p_{x}^{2} =\pi^* 2p_{y}^{2}\right), \sigma^* 2p_z^2$
B.O. $= \frac{1}{2} \left(10 -10\right)= 0, Ne_2$does not exist.
$ C_2 : \sigma1s^2 , \sigma^* 1s^2 , \sigma2s^2 ,\sigma^* 2s^2 , (\pi 2p_x^2 = \pi 2p_y^2)$
B.O $ =\frac{1}{2}\left(8 - 4 \right)= 2 , C_2$ exists.