This scatter plot maps atomic radius against first ionization energy for all elements. A clear inverse relationship emerges - larger atoms are easier to ionize.

The pattern reflects Coulomb's law: electrons farther from the nucleus experience weaker attraction and require less energy to remove. Cesium with the largest radius has the lowest ionization energy among stable elements. Conversely, helium with its tiny radius and tightly-held electrons has the highest. This relationship explains why metals on the left side of the periodic table are so reactive.