It was stated in a textbook that the first ionisation energy is

the minimum energy needed to remove one mole of electrons from one mole of gaseous atoms in their ground state

Is there a difference between ionisation energy and first ionisation energy?

  • $\begingroup$ There is a first, second, third, fourth, … ionisation energy. Does that answer your question? $\endgroup$ – Jan Sep 13 '17 at 11:05
  • $\begingroup$ @Jan not really. chemguide.co.uk/atoms/properties/moreies.html explains the successive ionisation energies with the equations, but ionisation energy isn't explained. $\endgroup$ – George Tian Sep 13 '17 at 11:17
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    $\begingroup$ Well, ionisation energy is the general term and first ionisation energy specifies. As you would expect from language. $\endgroup$ – Jan Sep 13 '17 at 11:24
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    $\begingroup$ en.wikipedia.org/wiki/Ionization_energy $\endgroup$ – Mithoron Sep 13 '17 at 14:09

There is no difference between "ionization energy" and "first ionization energy". Another definition from Wikipedia:

The ionization energy (IE) is qualitatively defined as the amount of energy required to remove the most loosely bound electron, the valence electron, of an isolated gaseous atom to form a cation.

Here it's more clear that they are the same, since "the most loosely bound electron" is a single electron, and each successive ionization only removes a single electron at a time.

Additionally, if one were to remove all electrons from an atom, it would be explicitly stated as "complete ionization".

  • $\begingroup$ From both your and my definitions, I can see a difference. Can I confirm that the difference is that ionisation energy removes electrons from ONE atom, while the first, second third... ionisation energy removes electrons from ONE MOLE of atoms? $\endgroup$ – George Tian Sep 14 '17 at 11:14
  • $\begingroup$ No. The definition of ionization energy is $\ce{X + \text{energy} -> X+ + e-}$, with nothing about atoms or moles. It's all about the units, which work out to be per mole. Units are consistent between all successive ionization energies. $\endgroup$ – pentavalentcarbon Sep 14 '17 at 12:27

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