Mg is 3 and they are two electrons in its outermost energy level. On the other hand, energy level of Ca is 4 and there are two electrons in its outermost level. In spite same number of electrons in their outermost levels, attraction between the nucleus and valence electrons of Mg is higher than that of Ca.
ionization energy than Mg. This is because it is lower in the periodic table. The added central electrons added over the extra period provide shielding in the center of the atom
