Question

Stability of the species $L{i}_2,L{i}_2^{-},$ and $L{i}_2^{+}$ increases in the order of

• A. $L{i}_2<L{i}_2^{+}<L{i}_2^{-}$
• B. $L{i}_2^{-}<L{i}_2^{+}<L{i}_2$
• C. $L{i}_2<L{i}_2^{-}<L{i}_2^{+}$
• D. $L{i}_2^{-}<L{i}_2<L{i}_2^{+}$

Answer 1

Answer: (B)

$L{i}_2(3+3=6)=\sigma 1s^2,{\sigma }^{\ast }1s^2,\sigma 2s^2$
Bond order $=\frac{4-2}{2}=1$
$L{i}_2^{+}(3+3-1=5)=\sigma 1s^2{,}_{\sigma }^{\ast }1s^2,\sigma 2s^1$
Bond order $=\frac{3-2}{2}=\frac{1}{2}=0.5$
$L{i}_2^{-}(3+3+1=7)=\sigma 1s^2,{\sigma }^{\ast }1s^2,\sigma 2s^1$
Bond order $=\frac{4-3}{2}=\frac{1}{2}=0.5$
Stability order is $L{i}_2^{-}<L{i}_2^{+}<L{i}_2$ ( because $L{i}_2^{-}$ has more
number of electrons in antibonding orbitals which
destabilises the species).