i know that if you want to figure out how many electrons an atom has on its outer ring (valence?), its 1 for group 1 (eg Na), 2 for group 2 (eg Mg), all the way to 7 for halogens and 8 for noble gases. however, how do you figure it out for transition metals in the middle? for example, Copper would have an electron configuration of 1s2 2s2 2p6 3s2 3p6 4s2 3d9 so would this have 2 because there is only 2 on its outside ring (n=4)? what about the 17 electrons in the 3 energy level? is it possible for any atom to have more than 8 on its outside ring? what about the octet rule? how do you use it to figure out its charge? again, groups 1 through 8 are reasonable and make sense since you add or subtract electrons to gain the octet. but what about transition metals again? how can you use the electron configuration to figure out what charge their atoms will be? thanks.