16 electrons. Sulfur. Kinda hard to explain but if you just look at the periodic table period 3 (row 3) the s shell is the first two groups and p is the 6 on the right. 3s1 = sodium, 3s2 = magnesium, 3p1 = aluminum... 3p4 is sulfur. Solution 16 electrons. Sulfur. Kinda hard to explain but if you just look at the periodic table period 3 (row 3) the s shell is the first two groups and p is the 6 on the right. 3s1 = sodium, 3s2 = magnesium, 3p1 = aluminum... 3p4 is sulfur..