Solution

$He_2$: electronic configuration $\sigma 1s^2\,\sigma^*1s^2$ Bond order $= \frac{1}{2}(N_b - N_a) = \frac{1}{2}(2 - 2) = 0$ Since the bond order is zero, the $He_2$ molecule does not exist.

Concept molecules that cannot exist (bond order zero)

Molecular Orbital Theory - Bond Order in past papers

5 questions from this chapter have appeared across 5 exam years.