A helium nucleus was presumed to be composed of four protons plus two "nuclear electrons" (electrons bound inside the nucleus) to cancel two of the charges.

In this model, incident electromagnetic waves forced an electron bound to an atom to oscillate.

It is a property of a collective state in which electrons bind magnetic flux lines to make new quasiparticles, and excitations have a fractional elementary charge and possibly also fractional statistics.

Usually this electron is in the valence band, and is tightly bound in covalent bonds between neighboring atoms, and hence unable to move far.

In the same manner, a change of mass occurs as an electron binds to a proton.

These reach right down into the energy regions where one would expect electrons to stay bound to individual atoms.

Eventually, atoms begin to form as free electrons bind to nuclei.

It's the same thing that happens in an atom (otherwise every ground state atom would be a bunch of 1s electrons bound to a nucleus).

It falls off relatively slowly with distance (like 1 over the distance squared) and so holds the electrons bound to the nucleus.

The electrically neutral atom contains a single positively charged proton and a single negatively charged electron bound to the nucleus by the Coulomb force.