Check with you local welding gas supplier and ask if they have literature published by Praxair. I recall they had an excellent brochure on the subject that discussed just what you are asking about. That brochure even discusses instability of electrons in the outer orbital shells but it does so in layman's terms. Unfortunately, I won't be back in the office for a week (actually it is fortunate because of vacation) so I can't tell you the book title right now, but if you don't find the info, I'll get back to you next week.
Possibly, you can contact Praxair directly but I don't have the address.

Chet Guilford