More sleepless pondering about pedagogical steps toward extra-classical
thinking :
The 17 planetary electrons in a neutral Chlorine atom are trapped in the
potential energy well of the 17 proton nucleus, producing a stable
neutral atom. However an even more stable ION is produced if another
electron is added to complete the outer shell and mimic a noble gas
(Argon) configuration. The ion CL- is 3.8 eV lower in energy than the
neutral Cl atom. (Eisberg/Resnick, Quantum Physics, pg 454)
Students who have had Chemistry (not a few) are used to this favoring of
"closed shells" over electrical imbalance - ie in Chemistry they have
already lept ahead to thinking beyond the scope of our classical
electromechanics (they rely on a lot of QM in elementary chemistry).
I hope this helps, more than it might drive you wild!