How does ionization energy change from lithium to cesium?

In the periodic table, the ionization energy—the energy required to remove an electron from an atom—decreases as you move down the group of alkali metals from lithium to cesium.12

Specifically, the first ionization energy drops from 520.2 kJ/mol for lithium to 375.7 kJ/mol for cesium. This trend occurs because, as you move down the group, the valence electron is located in an orbital that is increasingly farther from the nucleus. Because this electron is at a greater distance, it is less strongly held by the positive charge of the nucleus, making it easier to remove. Consequently, cesium is more likely to lose its valence electron than lithium, reflecting the general rule that metals at the bottom of a group have lower ionization energies and are more chemically active than those at the top.12