Question:
According to molecular orbital theory, which of the following is true with respect to $\mathrm{Li}_{2}^{+}$and $\mathrm{Li}_{2}^{-}$?
Correct Option: , 3
Solution:
Electronic configuratios of $\mathrm{Li}_{2}^{+}$and $\mathrm{Li}_{2}^{-}$:
$\mathrm{Li}_{2}^{+}: \sigma 1 \mathrm{~s}^{2} \sigma^{*} 1 \mathrm{~s}^{2} \sigma 2 \mathrm{~s}^{1}$
$\mathrm{Li}_{2}^{-}: \sigma 1 \mathrm{~s}^{2} \sigma^{*} 1 \mathrm{~s}^{2} \sigma 2 \mathrm{~s}^{2} \sigma^{*} 2 \mathrm{~s}^{1}$
Now,
Bond order of $\mathrm{Li}_{2}^{+}=\frac{1}{2}(3-2)=\frac{1}{2}$
Bond order of $\mathrm{Li}_{2}{ }^{-}=\frac{1}{2}(4-3)=\frac{1}{2}$
Here, both $\mathrm{Li}_{2}^{+}$and $\mathrm{Li}_{2}^{-}$have positive bond order, thus both are stable.