Question

In which of the following processes, the bond order has increased and the magnetic behaviour has changed?

• A. $C_2^{+}\to C_2$
• B. $N{O}^{+}\to NO$
• C. $O_2\to O_2^{+}$
• D. $N_2\to N_2^{+}$

Answer 1

The correct option is A $C_2^{+}\to C_2$

(a) $C_2^{+}\to C_2$
$B.O.=1.5B.O.=2$
$\text{paramagnetic}\text{diamagnetic}$
$C_2^{+}={\sigma }_{1s^2}{\sigma }_{1s^2}^{\ast }{\sigma }_{2s^2}{\sigma }_{2s^2}^{\ast }{\pi }_{2p_x^2}={\pi }_{2p_y^1}$
$\text{Bond order}=\frac{N_b-N_a}{2}$
$=\frac{7-4}{2}=1.5$ (Paramagnetic)
$C_2={\sigma }_{1s^2}{\sigma }_{1s^2}^{\ast }{\sigma }_{2s^2}{\sigma }_{2s^2}^{\ast }{\pi }_{2p_y^2}={\pi }_{2p_y^2}$
$\text{Bond order =}\frac{N_b-N_a}{2}$
$=\frac{8-4}{2}=2$ (diamagnetic)
(b) No ($s-p$ mixing)
$\Rightarrow {\sigma }_{1s}^2{\sigma }_{1s}^{\ast 1}{\sigma }_{2s}^2{\sigma }_{2s}^{\ast 2}{\pi }_{2px}^2={\pi }_{2py}^2{\sigma }_{2pz}^2{\pi }_{2py}^{\ast }$
$B.O.=\frac{10-5}{2}=2.5$
For $N{O}^{+}$,
$B.O=\frac{10-4}{2}=3$
(c) $O_2$ ( no $s-p$ mixing)
$\Rightarrow {\sigma }_{1s}^2{\sigma }_{1s}^{\ast 2}{\sigma }_{2s}^2{\sigma }_{2s}^{\ast 2}{\pi }_{2px}^2={\pi }_{2px}^2{\pi }_{2py}^{\ast 2}{\pi }_{2px}^{\ast 1}={\pi }_{2py}^{\ast 1}$
$B.O.=\frac{10-6}{2}=2$
$O_2^{+};B.O.=\frac{10-5}{2}=2.5$
Both $O_2$ and $O_2^{+}$ are paramagnetic
(d) $N_2$
$\Rightarrow {\sigma }_{1s}^2{\sigma }_{1s}^{\ast 2}{\sigma }_{2s}^2{\sigma }_{2s}^{\ast 2}{\pi }_{2px}^2={\pi }_{2py}^2{\sigma }_{2pz}^2$
$B.O.=\frac{10-4}{2}=3$
$N_2^{+};\Rightarrow {\sigma }_{1s}^2{\sigma }_{1s}^{\ast 2}{\sigma }_{2s}^2{\sigma }_{2s}^{\ast 2}{\pi }_{2px}^2={\pi }_{2py}^2{\sigma }_{2pz}^{1}B.O.=\frac{9-4}{2}=2.5$