Question

According to molecular orbital theory, which of the following will not be a viable molecule ?

• A. $He^{2+}_2$
• B. $He^{+}_2$
• C. $He^{-}_2$
• D. $He^{2-}_2$

Answer 1

Answer: (D)

$He^{2-}_2$

Answer 2

Electronic configuration of $H _{2}{ }^{2-}=\left(\sigma s ^{2}\right)\left(\sigma^{*} s ^{2}\right)$
Bond order of $H _{2}^{2 \ominus}=\frac{ N _{ b }- N _{ a }}{2}=\frac{2-2}{2}=0$.
If a bond order of zero is obtained, that means that the molecule is too unstable and so it will not exist.
Hence, $H _{2}^{2 \ominus}$ does not exit, due to zero bond order.