Knowledge database: Basics: Ionization energy

Ionization energy is the amount of energy that is needed to subtract one electron from an atom. The alkali metals have the lowest ionization energies, which means that they easily release electrons because a minimal level of energy is needed to break out an electron. It is also important to mention that the ionization energy decreases within the same group in the periodic system (while the atomic number and atomic volume values are increased). This means that the outer electrons in the larger atom were not so strongly bound to the nucleus, as were the outer electrons in the smaller atom. Furthermore, one can see that the ionization energy within the same period increases (while the atomic number values are increased), although not quite continually. The ionization energies have largest values in the group of noble gases, which is logical because they have the ideal, i.e. most stable electron configuration.

Range of ionization energy values in the PTE.