ionization energy
nounUK /ˌaɪənaɪˈzeɪʃən ˈenədʒi/
US /ˌaɪənəˈzeɪʃən ˈenərdʒi/
The energy you need to pull an electron away from an atom.
Sodium has a low ionization energy, so it gives up its outer electron easily.
OTHER MEANINGS
2. The minimum energy required to remove the most loosely bound electron from a neutral atom in the gas phase.
The first ionization energy of hydrogen is about 13.6 electron volts.
3. The energy needed to remove a second or later electron from an already charged ion.
The second ionization energy of magnesium is much higher than its first.
4. A measure of how tightly an atom holds its electrons, used to predict chemical reactivity.
Noble gases have very high ionization energies, which is why they rarely react.