The energy used to remove a stable ion from an atom.

the energy required to remove an electron from a species. The first ionization energy is the energy required to convert a neutral species to a singly charged anion (e.g., Cl = Cl-). The second ionization energy is the energy required to remove an additional electron (e.g., Mg+ = Mg+).

the energy required to remove an electron from a gaseous atom. (see electron affinity, electronegativity)

Energy required to remove an electron from a specific atom.

The energy change accompanying the loss of an electron from a species.

energy required to remove an electron from an atom (creating a cation)

Ionization energy is the minimum energy required to remove an electron from an isolated atom or molecule (in its vibrational ground state) in the gaseous phase.

The minimum amount of energy required to remove the most loosely held electron of an isolated gaseous atom or ion.

the quantity of energy required to remove an electron from a gaseous atom or ion.