an electron that is in the highest occupied energy level of an atom ??? ??? ??? alkali metals the elements in Group 1A of the periodic table, not including hydrogen ??? ??? ??? alkaline earth metals the elements in Group 2A of the periodic table ??? ??? ??? halogens the elements in Group 7A of the periodic table ??? ??? ??? noble gases the elements in Group 8A of the periodic table ??? ??? ??? nu