Electron Shells and Electron Distribution
An electron shell is an orbit of electrons around the nucleus of an atom. The electrons in the outermost shell establish the atom's chemical properties. Each electron shell can house only a set number of electrons. Thus, each shell must fill to capacity before electrons can be added to the outer shell. All elements seek to have a full outer shell of electrons (valence 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 on out to the outermost. Electrons in outer shells typically possess higher energy. These outer shell electrons travel further from the nucleus than electrons in inner shells. This is why the electrons in the outermost shell are more essential in determining how the atom reacts chemically and behaves as a conductor, since the attraction of the atom's nucleus for them is weaker and more easily ignored. An element's reactivity is basically dominated by the electron configuration.
Electron configuration refers to how the electrons of the atom are arranged. An atom's electron configuration is highly dependent on its electron distribution, which is the function that assigns the number of electrons per unit volume of phase space.