I have seen similar posts, but I haven't seen what seems to be a clear and direct answer. Why do only a certain number of electrons occupy each shell? Why are the shells arranged in certain distances from the nucleus? Why don't electrons just collapse into the nucleus or fly away? It seems there are lots of equations and theories that describe HOW electrons behave, predictions about WHERE they may be located, etc. But hard to find the WHY and causality behind these descriptive properties. Thank you! Please be patient with me, new to this forum and just an amateur fan of physics.