Where on the table would a group’s ionization energy be the greatest?

Ionization energy is the amount of energy required to remove an electron from a gaseous atom or ion. In the periodic table, the ionization energy tends to increase as you move from left to right across a period and from bottom to top within a group.

Therefore, the greatest ionization energy in a group would be found at the top of a group (also known as a family). This is because elements at the top of a group have their valence electrons closer to the nucleus and the atomic radius is smaller, resulting in a stronger attraction between the nucleus and the valence electrons. Hence, more energy is required to remove an electron from these elements.

For instance, in Group 1 (the alkali metals), hydrogen has the highest ionization energy, whereas in Group 17 (the halogens), fluorine has the highest ionization energy. As you go down a group, each element has an additional electron shell, which increases the distance between the nucleus and the valence electrons, reducing the nuclear charge's effective pull on the valence electrons and thus decreasing ionization energy.