Ionization energy

The ionization energy (symbol: E_i) is the energy required to remove an electron from a neutral atom or molecule to form a positively charged ion. Ionization potential is an older name for the same quantity.

For both historical and technical reasons, ionization energies are often quoted in electronvolts; for chemical purposes, it is often more convenient to use molar ionization energies expressed in kJ mol⁻¹.

Data pages

• First ionization energies of the elements
• Ionization energies of the elements (Z = 1–30)

See also

• Electron affinity