Each energy level (shell) has more subshells available to it: 1  The first shell only has the s subshell â¹ 2 electrons. 2  The second shell has the s and p subshells â¹ 2 + 6 = 8 electrons. 3  The third shell has the s, p, and d subshells â¹ 2 + 6 + 10 = 18 electrons. 4  The fourth shell has the s, p, d, and f subshells â¹ 2 + 6 + 10 + 14 = 32 electrons.