When elements are atoms and when they exist as ions, it is the number of electrons that differentiates them.
Orbits around the shell.
Heisenberg uncertainty principle : it is not possible to determine where an electron currently is and where it will move next.
Highest probability of finding it in the electron cloud.
An electron is a tiny particle, smaller than an atom, with a negative electric charge, with hardly any mass. It is too small to see even with an electron microscope. Electrons aren’t made of anything else; you can’t break them apart into anything smaller.