 The potential is an intensive property and it is measured by "volt"; whereas the energy is an extensive property expressed by "eV" or "kJ/mole".As one progresses down a group on the periodic table, the ionization energy will likely decrease since the valence electrons are farther away from the nucleus and experience a weaker attraction to the nucleus's positive charge.There will be an increase of ionization energy from left to right of a given period and a decrease from top to bottom.