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Why does the He₂ molecule not exist according to MO theory?
AHe atoms repel each other electrostatically
BHe₂ would have bond order zero — both bonding and antibonding orbitals are filled with 2 electrons each, so bonding is cancelled
CHe atoms are too small
DHe has no valence electrons
Answer & Solution
Correct answer: B. He₂ would have bond order zero — both bonding and antibonding orbitals are filled with 2 electrons each, so bonding is cancelled
He₂ MO config: (σ1s)² (σ*1s)². Bond order = ½(2 − 2) = **0** — antibonding cancels bonding → no net bonding → He₂ does not exist as a stable molecule.
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