Question

As per molecular orbital theory, bond order of $Li _{2}$ is $x$ and bond order of $Li _{2}^{-}$is $y$. The value of $(x-y)$ is____.

Answer 1

$Li _{2} \Rightarrow \sigma 1 s ^{2} \,\sigma^{*} 1 s ^{2} \,\sigma 2 s ^{2}$
Bond order $=\frac{ N _{ b }- N _{ a }}{2}$
$=\frac{4-2}{2}=1$
$\therefore x=1$
$Li _{2}^{-} \Rightarrow \sigma 1 s ^{2} \,\sigma^{*} 1 s ^{2}\, \sigma 2 s ^{2} \,\sigma^{*} 2 s ^{1}$
Bond order $=\frac{4-3}{2}=\frac{1}{2}=0.5$
$\therefore y=0.5$
$\therefore (x-y)=(1-0.5)=0.5$