In atoms charges are neatly separated. Instead of pairing which seems natural they all stick together with their peers.

What drives this peer behaviour? Why is it stable?

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    $\begingroup$ Are you asking why the electrons don’t fall into the nucleus? $\endgroup$ – G. Smith Jan 13 at 17:51
  • $\begingroup$ He is asking why electrons stick to each other :-) $\endgroup$ – Vladimir Kalitvianski Jan 13 at 17:57
  • $\begingroup$ Well, in most atoms you do have simple pairing, since most atoms are hydrogen. ;) Pairing in heavier atoms is trickier because of the huge mass difference between electrons & protons, and the constraints imposed by Pauli exclusion. Hopefully, someone will write an answer that explains this properly. $\endgroup$ – PM 2Ring Jan 13 at 19:22
  • $\begingroup$ Your point is interesting, yes, most atoms are Hydrogen, but why do the electrons stay outside like spectators when it comes to fusion? $\endgroup$ – Johannes Maria Frank Jan 14 at 16:45
  • $\begingroup$ At typical fusion temperatures the nuclei & electrons have very high kinetic energy. And because the electrons are so light they have much higher speeds than the nuclei. There's little chance for the nuclei & the electrons to combine stably under those conditions. $\endgroup$ – PM 2Ring Jan 15 at 9:49

The nuclear forces are much stronger than the electromagnetic forces, but their range is much shorter. So nucleons very close together are pulled together by the nuclear forces, and less strongly pushed apart by the Coulomb force.

The electrons, on the other hand, are attracted by the oppositely charged nucleus, here, the Coulomb force of the core is stronger than the Coulomb force of the other electrons. But the electron interaction is strong enough to keep them on different levels, so to say.

Fusion usually occurs under very high temperatures, where everything is in a plasma state, so naturally electrons are "standing aside", only the reaction cross-sections of the cores matter for the fusion process. When the temperature is high enough, the cores have enough kinetic energy to overcome the Coulomb barrier on a direct hit. The cores pass their barrier and a sort of friction occurs, which causes internal excitation. The system is heating up. As long as the reaction partners are "mixed", i.e. within each others boundary region, mass transfer can occur from one to the other. Depending on the reaction time, more or less mass is transferred/exchanged. During the process the system is rotating. Eventually the two partners will split up again. During this reaction, their kinetic energy was mainly transformed into internal excitation and they exchanged mass.

  • $\begingroup$ Your argument lacks the fact that the Coulomb force closer is always much stronger than the one more distant. And the atom is huge, so the force of the core is relatively low compared to the force of the peers. The strong force is not so much stronger, it even doesn't suffice to make a DiProton core. Yes, it is known that it keeps the core together, but that already assumes there are no electrons in the nearby when the strong force hits. The point made by PM 2Ring is interesting but it still leaves the question why the electrons are not caught on fusion. $\endgroup$ – Johannes Maria Frank Jan 14 at 16:44
  • $\begingroup$ Oh, you are asking on a much higher level than I thought. So I apologise for my rather basic answer. I added another section to my answer. $\endgroup$ – kalle Jan 14 at 17:16

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