Ionization energy (IE) is the energy required to remove an electron from an atom. As atomic radius increases, the valence electrons get farther from the nucleus. How do you think an atom's size will affect its ability to hold on to its valence electrons? Why?

The larger the atom, the lesser the tendency for the atom to withhold its valence electrons.

Explanation:

The size of an atom is usually estimated in terms of its atomic radius. Across the period in the periodic table, the atomic radius decreases progressively from left to right. This is due to the progressive increase in the nuclear charge (i.e., the number of protons in the nucleus) without an attendant increase in the number of electronic shells.

Similarly, down the group, the atomic radius increases progressively from top to bottom due to the successive number of electrons' shells.

Thus, the larger the atom's radius, the smaller the Ionization energy because of the increasing shielding effect of inner shell electrons on the electron to be removed from the nuclear attraction.

Finally, we can conclude that as the atom becomes larger, the tendency to withhold the electrons on the outer shell decreases due to distance and the shielding/ screening effect.