text: The Cadmium atomic number is 48\nFor the first 4 energy levels<shells>; max # of electrons = 2 * (n^2)\nso you have in n=1 -> 2 electrons; n=2 -> 8 electrons; n = 3 -> 18; n = 4 -> 32\n\nthere are (2+8+18) = 28 electrons taken on the first 3 shells; There is still    48-32 = 16 electrons that will be in the 4th shell