Atkins's What is Chemistry: the role of electrons in determining the atom's various liasons

A complete cloud layer of electrons imparts energy advantages to atoms.  Atoms with very few electrons in the outermost layer may shed them to form cations and atoms with many electrons in the outermost layer will tend to grab a few more from another atom to form anions.  Atoms which want more electrons can share them.  The word ion is Greek for going while the prefixes an and cat are Greek for up and down, referring to the opposing responses of opposite charge particles to an electric field.  Whenever I introduce the terms anion and cation to my students, I always follow it with "Don't ask me where those words came from.."  Now, I know.