or ionization energy
Amount of energy required to remove an electron from an isolated atom or molecule .
There is an ionization potential for each successive electron removed, though that associated with removing the first (most loosely held) electron is most commonly used. The ionization potential of an element is a measure of its ability to enter into chemical reactions requiring ion formation or donation of electrons and is related to the nature of the chemical bonding in the compounds formed by elements. See also binding energy , ionization .