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geekpeeps t1_iy9gdbf wrote

Reply to comment by drafterman in ELI5: why 2 hydrogen atoms hold more energy and less mass than 1 helium atom? by TheLapisBee

And the two hydrogens (now a molecule) have more energy because of the intermolecular forces - as the hydrogens oscillate (kind of) their movement towards and away from one another is more energetic than the helium atom just on its own.

Edit: there is a quantum chemistry exercise in calculating the variations in energy between a hydrogen 2+ molecule (two protons sharing an electron) and 3D mapping the changes. It was much more difficult without the internet and digital graphing available nowdays.

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Any-Growth8158 t1_iy9h94s wrote

I'd assume that diatomic hydrogen having more energy than a helium atom is discounting the mass energy of the neutrons...

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geekpeeps t1_iy9jsss wrote

It’s about the interactions between the two as they move away and toward each other. Helium will have complete a electron shell and the nucleus is basically at rest. Hydrogen as (H - H) is stable but reactive. Helium is inert.

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