What is so special about having 8 electrons in a shell?
Although there are studies of the octet rule that show variations in it and such, I’ve never really seen an explanation of why 8 electrons is so stable. One factor that stable orbits have an even number of electrons (2, 8, 18, 32…) is that it would allow opposite spin directions for the electrons. Another factor may be the optimum separation between electrons. For the smaller inner shell, 2 electrons is the most allowed, otherwise they would get too close to each other. For the next shell, the circumference would allow a maximum of 8. This is a very rough concept, because the shell system is more complex, with sub-shells and electrons not as particles but as clouds or strings. Anyway, I believe that the spin and optimum separation are important factors in the octet rule.
