A simple easy to teach description of how many electrons fill each of the shells of an atom is the "2 8 8 2 " configuration. The steps after this require students learn a new trick as it goes "2 8 9 2" all the way to "2 8 18 2" not "2 8 8 18" as is being taught. Listen to a Quantum Physicists trying to make sense of what is going on in the classroom.
