The Halogens; Alkaline earth metals group (A) tends to have the highest ionization energy while the Alkali metals group tends to have the lowest ionization energy. Ionization energy is the energy required to move an electron from orbiting around an atom until it is no longer associated with the atom. The position of elements on the periodic table indicates the level of ionization energy. The ionization energy of an element increases when you move across a period in the periodic table This is because the electrons are held together with a stronger bond than others.
