This file is from Wikimedia Commons and may be used by other projects.
The description on its file description page there is shown below.
Summary
DescriptionIonization energies of atoms - labeled - atomic orbital filling indicated.svg
English: Ionization energy is the minimal energy needed to remove an electron from a neutral atom. The ionization energies grow within a period in the periodic table of elements from alkali metals to noble gases and reach local maxima as each of the s, p, d and f orbitals fill.
Date
Source
Own work
Based on File:Ionization energies.svg by RJHall and Hardwigg. According to them, data for this diagram comes from Martin, W. C.; Wiese, W. L. (1996) Atomic, Molecular, & Optical Physics Handbook, American Institute of Physics, ISBN156396242X.
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.