How are atomic size and ionization energy related?

Ionization energy is the amount of energy needed to extract the most loosely held electron from a gaseous atom or ion; it decreases down the family tree and increases over time. Therefore, as atomic size decreases, so does ionization energy. Atomic size is the distance between the nucleus and the valence shell.

Atomic size and ionization energy are inversely related. As atomic size increases, ionization energy decreases, and vice versa. This relationship exists because ionization energy is the energy required to remove an electron from an atom, while atomic size refers to the distance between the nucleus and the outermost electron shell. When the atomic size is larger, the outermost electrons are farther from the nucleus, experiencing less attraction and requiring less energy to remove. Conversely, when the atomic size is smaller, the outermost electrons are closer to the nucleus, experiencing stronger attraction and requiring more energy to remove. Therefore, as atomic size increases, ionization energy decreases, and as atomic size decreases, ionization energy increases.