Ionization energy

Energy needed to remove an electron

In physics and chemistry, ionization energy (IE) (American English spelling), or ionisation energy (British English spelling) is the minimum energy required to remove the most loosely bound electron(s) (the valence electron(s)) of an isolated gaseous atom, positive ion, or molecule. The first ionization energy is quantitatively expressed as X(g) + energy ⟶ X+(g) + e− where X is any atom or molecule, X+ is the resultant ion when the original atom was stripped of a single electron, and e− is the removed electron. Ionization energy is positive for neutral atoms, meaning that the ionization is an endothermic process.

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