Not sure about the energy point. I assume you mean when attaching to oxygen to make water?

Mass though, it has to do with the amount of neutrones. Helium needs more neutrons to stabilize itself thus adding more weight to it. Normal Helium also can not for bonds meaning it doesn’t react thus can’t produce or take energy because it’s electron ring is full of electrons. No pressure to fill the ring with bonding to another element

Two hydrogen atoms have less mass than one helium atom because helium atoms have neutrons in addition to protons while hydrogen atoms just have protons.

If you’re asking about nuclear fusion, the process actually begins with four hydrogen atoms, two of which end up converted to neutrons during the reaction.

Two electrons and two positrons are ejected and then annihilated along the way, releasing a considerable amount of energy.

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.

To help you understand exactly what happens, you need 4 hydrogens to smash together with tremendous energy, typically due a massive amount of gravity pulling them together.

Each hydrogen atom has 1 proton, but when you smash 4 of them together 2 of the protons "morph" into neutrons. Neutrons are slightly more massive than protons, so all things being equal you can understand why 1 helium should have slightly more mass than 4 hydrogens.

What's also happening is part of that energy in the first place that fused the hydrogens in helium got "solidified" into mass of helium, like energy gets stored in a battery. That energy can be pulled back out if you get the helium atom to decay, this is literally how nuclear energy and nuclear bombs work.

Not sure where you are getting the "more energy" bit from. Either you're thinking about how we can use hydrogen as fuel and not helium (which comes down to electron configurations, hydrogen is "unhappy" and that unhappiness creates a desire to participate in chemistry, hence boom.) Or your thinking of the original energy required to fuse the hydrogens in the first place, and that usually comes from gravity.

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

[deleted]

So fusion basically uses gravity to turn mass into energy?

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.

You have it backwards - radioactive decay turn mass into energy. (that's literally what E=mC^(2) means). The conversion multipler of mass to energy is C^(2) so a huge amount of energy makes a teeensy tiiny bit of mass, or a tiny bit of mass makes a HUGE amount energy.

Fusion in stars is complicated, is uses not-ELI5 type things like the "weak nuclear force", and yes, gravity, to convert energy into mass and energy into different mass and energy. The trick in the Sun is it has a tremendous amount of Gravity which kick-starts the process and creates a large net-output of energy (sunlight and other radiation). In something a fusion powerplant the problem is you don't have that gravity source so you need a large energy input in the form of heat in the place of gravity. Currently, it takes more energy for us to create fusion that we get out so it's not a sustaining reaction like the Sun is.

This answer is wrong. Deuterium and tritium are just as much hydrogen as protium is, and similarly helium includes helium-3 as well as helium-4. Further, deuterium has a mass of 2,014,101.777844 µu, while helium-4 has a mass of 4,002,603.254130 µu, so we can see that even when the number of protons and neutrons line up, the mass is not the same.

As you can see from the numbers I just posted, you and OP (u/TheLapisBee) are actually also backwards in that 2 ^(2)H atoms have more mass than 1 ^(4)He atom.

Oh wow! I was very much wrong... So where does this mass come from in the fusion process?

Sans clarification/qualification, it is not unreasonable to treat hydrogen as hydrogen-1 and helium as helium-4.

Oh thanks!

> Neutrons are > slightly > more massive than protons, so all things being equal you can understand why 1 helium should have > slightly > more mass than 4 hydrogens.

Actually, the helium produced in the proton-proton chain has less mass than the constituent hydrogens. The difference is about 23 MeV, which goes into the mass and energy of the byproducts (neutrinos and gamma radiation).

>So where does this mass come from in the fusion process?

The product has less mass than the ingredients. Mass is being lost, not gained, so the question is where does the mass go.

The answer to where the mass goes is that it goes to the energy of the radiation being emitted.

Ohhhh right, got a bit confused, thanks! Also how do u highlight what part of my comment you reply to?

Depends if you're using markdown or the "Fancy Pants Editor". In Markdown you simply put a > at the start of the paragraph, like this:

>This is a quote

In the "Fancy Pants Editor" you have to select the quote block option through the GUI.

[deleted]