The ionization energy or ionization potential is the energy necessary to remove an electron from the neutral atom. It is a minimum for the alkali metals which have a single electron outside a closed shell. It generally increases across a row on the periodic maximum for the noble gases which have closed shells. For example, sodium requires only $\pu{496 kJ/mol}$ or $\pu{5.14 eV/atom}$ to ionize it while neon, the noble gas immediately preceding it in the periodic table, requires $\pu{2081 kJ/mol}$ or $\pu{21.56 eV/atom}$. The ionization energy is one of the primary energy considerations used in quantifying chemical bonds.