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In which pair are BOTH species not expected to exist?

1. H2+, He2-
2. H2-, He2-
3. H2(2+), He2
4. H2-, He2+

Correct answer: H2(2+), He2

Solution

H2(2+) has no electrons (bond order 0) and He2 has equal bonding and antibonding electrons (bond order 0), so neither exists; the other listed ions have nonzero bond order.

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