How does the trend in atomic size differ from the trend in ionization energy? Explain.

The distance between the nucleus and the valence shell is measured in an atomic size. The energy necessary to remove the most loosely held electron from a gaseous atom or ion isionization energy. Ionization energy rises throughout time and falls as the family descends. As the size of an atom becomes greater, the ionization energy drops within a group.

Ionization energy is required to remove one electron from a higher energy level from one mole of gaseous atoms. The distance between the nucleus and the outermost shell is measured in atomic size. As electrons go closer to an atom's nucleus, an atomic size shrinks as ionization energy rises.

As a result, the atomic size trend is the polar opposite of the ionization energy trend.