Chemistry - CHEMICAL BONDING Question with Solution | TestHub

$$${\text{Li}}_2^{-}<{\text{Li}}_2^{+}<{\text{Li}}_2$
Bond order$\propto$stability of species
${\mathrm{Li}}_2=\mathrm{\sigma }1{\mathrm{s}}^2<\stackrel{*}{\mathrm{\sigma }}1{\mathrm{s}}^2<\mathrm{\sigma }2{\mathrm{s}}^2;\mathrm{B}.\mathrm{O}=\frac{4-2}{2}=1$
${\mathrm{Li}}_2^{-}=\mathrm{\sigma }1{\mathrm{s}}^2<\stackrel{*}{\mathrm{\sigma }}1{\mathrm{s}}^2<\mathrm{\sigma }2{\mathrm{s}}^2<\stackrel{*}{\mathrm{\sigma }}2{\mathrm{s}}^1;\mathrm{B}.\mathrm{O}=\frac{4-3}{2}=0.5$
${\mathrm{Li}}_2^{+}=\mathrm{\sigma }1{\mathrm{s}}^2<\stackrel{*}{\mathrm{\sigma }}1{\mathrm{s}}^2<\mathrm{\sigma }2{\mathrm{s}}^1; \mathrm{B}.\mathrm{O}=\frac{3-2}{2}=0.5$
${\mathrm{Li}}_2^{+}$and${\mathrm{Li}}_2^{-}$both have same bond order, but${\mathrm{Li}}_2^{-}$has more number of electron in anti-bonding molecular orbitals (experience more inter electronic repulsion) and hence least stable among three species.