JEE MAIN - Chemistry (2019 - 9th January Morning Slot - No. 22)
According to molecular orbital theory, which of the following is true with respect to Li2+ and Li2$$-$$ ?
$$Li_2^ + $$ is unstable and $$Li_2^ - $$ is stable
$$Li_2^ + $$ is stable and $$Li_2^ - $$ unstable
Both are stable
Both are unstable
Explanation
$$Li_2^ + $$ (5 electrons) = $${\sigma _{1{s^2}}}\,\,\sigma _{1{s^2}}^ * \,\,{\sigma _{2{s^1}}}$$
$$Li_2^ - $$ (7 electrons) = $${\sigma _{1{s^2}}}\,\,\sigma _{1{s^2}}^ * \,\,{\sigma _{2{s^2}}}$$ $$\,\sigma _{2{s^1}}^ * \,$$
$$ \therefore $$ Bond order of $$Li_2^ + $$ = $${{3 - 2} \over 2}$$ = 0.5
Bond order of $$Li_2^ - $$ = $${{4 - 3} \over 2}$$ = 0.5
As both $$Li_2^ + $$ and $$Li_2^ - $$ has non-zero bond order, so both are stable.
$$Li_2^ - $$ (7 electrons) = $${\sigma _{1{s^2}}}\,\,\sigma _{1{s^2}}^ * \,\,{\sigma _{2{s^2}}}$$ $$\,\sigma _{2{s^1}}^ * \,$$
$$ \therefore $$ Bond order of $$Li_2^ + $$ = $${{3 - 2} \over 2}$$ = 0.5
Bond order of $$Li_2^ - $$ = $${{4 - 3} \over 2}$$ = 0.5
As both $$Li_2^ + $$ and $$Li_2^ - $$ has non-zero bond order, so both are stable.
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