behind organic chemisty is around electron shells http://en.wikipedia.org/wiki/18-Electron_rule http://en.wikipedia.org/wiki/Electron_counting http://en.wikipedia.org/wiki/Valence_shell Valence shells Main article: Valence electron The valence shell is the outermost shell of an atom . It is usually (and misleadingly) said that the electrons in this shell make up its valence electrons , that is, the electrons that determine