JEE Main 2013 — Chemistry Inorganic Chemistry

2013mcqmedium

Stability of the species ${\text{Li}}_{2} \text{,} {\text{Li}}_{2}^{-} \text{and} {\text{Li}}_{2}^{+}$ increases in the order of

Official previous-year question

Held on 7 Apr 2013 · Verified 6 Jul 2026.

Options

A
${\text{Li}}_{2} < {\text{Li}}_{2}^{-} < {\text{Li}}_{2}^{+}$
B
${\text{Li}}_{2}^{-} < {\text{Li}}_{2} < {\text{Li}}_{2}^{+}$
C
${\text{Li}}_{2} < {\text{Li}}_{2}^{+} < {\text{Li}}_{2}^{-}$
D
${\text{Li}}_{2}^{-} < {\text{Li}}_{2}^{+} < {\text{Li}}_{2}$

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Solution

${\text{Li}}_{2}^{-} < {\text{Li}}_{2}^{+} < {\text{Li}}_{2}$

Bond order $\propto$ stability of species

${\mathrm{Li}}_{2}=\sigma 1{s}^{2}<\overset{*}{\sigma }1{s}^{2}<\sigma 2{s}^{2} ; B.O=\frac{4-2}{2}=1$

${\mathrm{Li}}_{2}^{-}=\sigma 1{s}^{2}<\overset{*}{\sigma }1{s}^{2}<\sigma 2{s}^{2}<\overset{*}{\sigma }2{s}^{1} ; B.O=\frac{4-3}{2}=0.5$

${\mathrm{Li}}_{2}^{+}=\sigma 1{s}^{2}<\overset{*}{\sigma }1{s}^{2}<\sigma 2{s}^{1} ; B.O=\frac{3-2}{2}=0.5$

${\mathrm{Li}}_{2}^{+}$ 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.

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Options

${\text{Li}}_{2} < {\text{Li}}_{2}^{-} < {\text{Li}}_{2}^{+}$

${\text{Li}}_{2}^{-} < {\text{Li}}_{2} < {\text{Li}}_{2}^{+}$

${\text{Li}}_{2} < {\text{Li}}_{2}^{+} < {\text{Li}}_{2}^{-}$

${\text{Li}}_{2}^{-} < {\text{Li}}_{2}^{+} < {\text{Li}}_{2}$

Solution

${\text{Li}}_{2}^{-} < {\text{Li}}_{2}^{+} < {\text{Li}}_{2}$

Bond order $\propto$ stability of species

${\mathrm{Li}}_{2}=\sigma 1{s}^{2}<\overset{*}{\sigma }1{s}^{2}<\sigma 2{s}^{2} ; B.O=\frac{4-2}{2}=1$

${\mathrm{Li}}_{2}^{-}=\sigma 1{s}^{2}<\overset{*}{\sigma }1{s}^{2}<\sigma 2{s}^{2}<\overset{*}{\sigma }2{s}^{1} ; B.O=\frac{4-3}{2}=0.5$

${\mathrm{Li}}_{2}^{+}=\sigma 1{s}^{2}<\overset{*}{\sigma }1{s}^{2}<\sigma 2{s}^{1} ; B.O=\frac{3-2}{2}=0.5$

JEE Main 2013 — Chemistry Inorganic Chemistry

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JEE Main 2013 — Chemistry Inorganic Chemistry

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