The maximum number of electrons in the outer electron energy level of an atom is eight.
Atoms are most stable when they have eight electrons in their outer electron energy level.
The 7 horizontal rows on the Periodic Table represent the energy levels. 2n 2 l - represents the electron energy sublevel . The two columns on the left of the table represent the s sublevel. The six columns on the right of the table represent the p sublevel. The ten columns in the middle of the table represent the d sublevel.