Why do hydrogen atoms form a molecule but helium atoms do not?

Explanation:

In terms of old school electron shells - One Hydrogen atom on it's own has an empty shell, and therefore to fill the shell it needs another electron. In the case of Helium, it already has two electrons at the same energy level - so it cannot accept any new electrons i.e. it cannot form new bonds.

Hydrogen atoms can form a molecule as 2 hydrogen atoms together can result in a low energy combination of 2 electrons of the same energy level.

Explanation: Helium atoms already have 2 electrons of the same energy so therefore it cannot accept more.