What is the trend of ionization energy as you move down a group in the periodic table?

As you move down a group in the periodic table, ionization energy decreases. This trend occurs due to the increasing distance between the nucleus and the outermost electrons as you add more electron shells. As the number of shells increases, the outer electrons are farther away from the nucleus and experience greater shielding from the inner electrons. This reduced attraction to the nucleus makes it easier to remove an outer electron, resulting in a lower ionization energy.

Additionally, the increased size of the atoms down a group means that the outermost electrons are held less tightly, contributing further to the decrease in ionization energy. Understanding this trend is key to predicting the reactivity and chemical behavior of the elements as you delve deeper into group properties.