Trends in Ionization Energy in Alkali Metals

In a recent study, researchers investigated the chemical properties of various elements and their electron configurations. They observed that elements in the same group of the periodic table exhibit similar chemical properties due to their similar valence electron configurations. However, when comparing elements across periods, key differences were noted, particularly in the atomic radii and ionization energies. Consider the elements: Lithium (Li), Sodium (Na), and Potassium (K). As you move down the group from Li to K, how do the ionization energies change and what underlying principle explains this trend?