Question

Assuming that Hund’s rule is violated, the bond order and magnetic nature of the diatomic molecule $B_2$ is

• A. 1 and diamagnetic
• B. 0 and diamagnetic
• C. 1 and paramagnetic
• D. 0 and paramagnetic

Answer 1

Answer: (A)

The molecular orbital electronic configuration of ${\mathrm{B}}_2$ molecule is
$\sigma 1s^2{\sigma }^{\ast }1s^2\sigma 2s^2{\sigma }^{\ast }2s^2\pi 2p_x^1\pi 2p_y^1$
If however, the Hund's rule is violated, then the configuration would be :
$\sigma 1s^2{\sigma }^{\ast }1s^2\sigma 2s^2{\sigma }^{\ast }2s^2\pi 2p_x^2$
$\therefore B.O.=\frac{6-4}{2}=1$
Since, all the electrons are paired up, the molecule is diamagnetic.