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by chopin 2789 days ago
Hydrogen normally comes as a molecule (H2), not an atom.
1 comments

Correct, but also just as importantly the He atom has both a higher nuclear charge and a full valence shell, which pulls the electrons in more tightly. I’d have to look it up but I believe a single He is even smaller than atomic hydrogen or at least comparable.

Edit: looked it up and yes, helium is smaller than atomic hydrogen.