# Why are atomic nuclei protons and neutrons, and not electrons and neutrons or protons and neutrons

Wouldn't proton-electron nuclei be more stable since they attract each other and aren't just neutral to each other? What is the reason for this? I tried searching for an answer but couldn't find anything.

• You could start with looking up the strong force, this is the one responsible for attraction between nucleons. If you still have questions after that you can expand your question too – Triatticus Aug 28 at 17:15

### Proton and electron

A proton and an electron can indeed bind together. But the binding energy between these two is not big (only $$13.6$$ eV). This binding is caused by the electric Coulomb force between the oppositely charged proton and electron. By the way: This is the well-known hydrogen atom. This low-energy bond can easily be cracked, e.g. by ultraviolet light, by temperatures above $$10^4$$ K, or by colliding with other moderately fast atoms.

### Protons and neutrons

On the other hand: Protons and neutrons can also bind together. They prefer to bind to lumps with approximately 50% protons and 50% neutrons, and their binding energy is very large ($$\approx 8$$ MeV per nucleon). These are the well-known atomic nuclei. This binding energy is so big, because it is caused by the so-called nuclear force between the protons and neutrons. This high-energy bond is very hard to crack, e.g. by temperatures above $$10^{10}$$ K, or by hitting them with other very fast nuclei.

### Electron and neutron

Electron and neutrons do not bind together at all. There is no electric force between them because the neutron has no electric charge. And there is no nuclear force between them because the electron is not subject to the nuclear force.

• "appproximately 50% protons and 50% neutrons" is only true for small nuclei. In large nuclei, a significant higher number of neutrons than protons is favored (for example, lead-208, which has 82 protons and 126 neutrons, and is stable, unlike the state with 104 protons and 104 neutrons). – probably_someone Aug 28 at 18:05
• Also, there is still a small electromagnetic interaction between neutrons and electrons. At low energy, there can be a magnetic dipole-dipole interaction. And at higher energies, the electron can interact with the quarks in the neutron via deep inelastic scattering. You're probably correct that there wouldn't be a bound state, though (the dipole-dipole interaction is likely too weak, and deep inelastic scattering destroys the neutron in most cases). – probably_someone Aug 28 at 18:08