In the ground state, each atom of an element has two valence electrons. This element has a lower first ionization energy than calcium. Where is this element located on the Periodic Table?
The element is the Group IIA family.
It is a period or row that is energy level five or more, below calcium on the periodic table.
Two valence electrons places the element in the alkaline earth family or group II A along with calcium.
As atoms become larger, the valence electrons become farther away from the attraction of the nucleus. The inner shells of electrons shield the valence electrons of the outer shells.
Because of the shielding effect it becomes increasingly easier to remove electrons. The first ionization energy is the energy needed to remove one valence electron.
Because the first ionization energy is less than calcium's, the element must be larger and in the next energy shell. Calcium is in the fourth energy shell, so the element must be in the fifth, sixth, or seventh energy shells.
The fourth, fifth, sixth and seventh energy levels are found below calcium on the periodic table. So the element must be in group II A below level four.