# According to molecular orbital theory,

Question:

According to molecular orbital theory, which of the following is true with respect to $\mathrm{Li}_{2}^{+}$and $\mathrm{Li}_{2}^{-}$?

1. $\mathrm{Li}_{2}^{+}$is unstable and $\mathrm{Li}_{2}^{-}$is stable

2. $\mathrm{Li}_{2}^{+}$is stable and $\mathrm{Li}_{2}^{-}$is unstable

3. Both are stable

4. Both are unstable

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.