Question

The bond dissociation energy of $C_2\left(599kJmo{l}^{-1}\right)$ decreases slightly on forming $C_2^{+}\left(513kJmo{l}^{-1}\right)$ increases greatly on forming $C_2^{-}\left(818kJmo{l}^{-1}\right)$.
If true enter 1 else 0.

Answer 1

$C_2\left(12e\right)$ has molecular orbital electronic configuration as :
$\left(\sigma 1s{)}^2\right({\sigma }^{\ast }1s{)}^2\left(\sigma 2s{)}^2\right({\sigma }^{\ast }2s{)}^2\left(\pi 2p_y^2\right)\left(\pi 2p_z^2\right)\sigma 2p_x^0$
Bond-order $=\frac{Electronsin(bondingMO-anti-bondingMO)}{2}$
$=\frac{8-4}{2}=2$
$C_2\left(13e\right):\left(\sigma 1s{)}^2\right({\sigma }^{\ast }1s{)}^2\left(\sigma 2s{)}^2\right({\sigma }^{\ast }2s{)}^2\left(\pi 2p_y^2\pi 2p_z^2\right)\sigma 2p_x^0$
Bond-order $=\frac{9-4}{2}=1.5$
Electron is added to higher energy orbital $\left(\sigma 2p_x\right)$ and bond-order increases.
$C_2^{+}\left(11e\right):\left(\sigma 1s{)}^2\right({\sigma }^{\ast }1s{)}^2\left(\sigma 2s{)}^2\right({\sigma }^{\ast }2s{)}^2\left(\pi 2p_y^2\pi 2p_z^1\right)$
Bond-order $=\frac{7-4}{2}=1.5$
Electron is removed from lower-energy orbital and bond-order decreases. This bond-dissociation energy of $C_2^{+}$ is much lower than of $C_2^{-}$ in which bond-order is higher and also electron is added to higher energy orbital.