How would you describe the periodic trend the ionization of elements within a group?
Ionization energy decreases down a group.
• Down a group, the number of e- shells increases by 1. Therefore, the e- are farther and farther away from the nucleus, and do not feel its pull as strongly.
• More filled inner e- shells means an increased nuclear shielding. Therefore, outer e- are protected from the increased pull of the + nucleus. It becomes easier, down a group, to remove them.
• The nuclear charge (i.e. the # of p+) increases down a group, as the nucleus becomes more positive; however, the increased nuclear shielding reduces the increased pull of the nucleus.
Thus, the energy required to remove an e- from the outermost shell of a gaseous atom decreases down a group.