The Role Of Electrons
Electrons do not spin just anywhere around the nucleus. They are found in Shells or Energy levels. The arrangement of electrons in the shells is called the electron configuration of the atom. Each shell can only contain a fixed number of electrons, each shell much be filled before electrons can be added to the outer shell.
The electron shells are labeled K, L, M, N, O, P, and Q; or 1, 2, 3, 4, 5, 6, and 7; going from innermost shell outwards. Electrons in outer shells have higher average energy and travel farther from the nucleus than those in inner shells.
This makes them more important in determining how the atom reacts chemically and behaves as a conductor, because the pull of the atom's nucleus upon them is weaker and more easily broken.
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving the atom a net positive or negative electrical charge.