8 groups, 1 to 7 and most people call group 8 group 0 because the noble gases in group 0 have the outer electron shell full, so for example argon has 18 electrons, so it’s structure is 2.8.8 with its outer shell full. Also the number of the last shell defies what group it’s in, for example sodium is in group 1 so it’s structure is 2.8.1. Hope this helps.
