Editing Ionization energy (section)

====Ionization energy decreases when====
* Transitioning to a new period: an alkali metal easily loses one electron to leave an [[octet rule|octet]] or pseudo-[[noble gas configuration]], so those elements have only small values for IE.
* Moving from the s-block to the p-block: a p-orbital loses an electron more easily. An example is beryllium to boron, with electron configuration 1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>1</sup>. The 2s electrons shield the higher-energy 2p electron from the nucleus, making it slightly easier to remove. This also happens from [[magnesium]] to [[aluminium]].<ref>{{cite web |url=https://www.angelo.edu/faculty/kboudrea/periodic/trends_ionization_energy.htm |title=The Parts of the Periodic Table |last=Boudreaux |first=K.A. |date=August 13, 2020 |orig-date=July 26, 2006 |department=Department of Chemistry and Biochemistry |website=angelo.edu/faculty/kboudrea/<!--this is the real website, pls dont change--> |publisher=Angelo State University |location=2601 W. Avenue N, San Angelo, TX 76909, Texas |language=en |access-date=December 19, 2020 |via=angelo.edu |archive-date=July 10, 2022 |archive-url=https://web.archive.org/web/20220710025232/https://www.angelo.edu/faculty/kboudrea/periodic/trends_ionization_energy.htm |url-status=dead }}</ref>
* Occupying a p-subshell with its '''first''' electron with spin opposed to the other electrons: such as in nitrogen ({{nuclide|N|&nbsp;}}: 14.5 eV) to oxygen ({{nuclide|O|&nbsp;}}: 13.6 eV), as well as [[phosphorus]] ({{nuclide|P|&nbsp;}}: 10.48 eV) to [[sulfur]] ({{nuclide|S|&nbsp;}}: 10.36 eV). The reason for this is because oxygen, sulfur and selenium all have dipping ionization energies because of shielding effects.<ref>{{Cite web|date=2014-07-02|title=18.10: The Group 6A Elements|url=https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_(Zumdahl_and_Decoste)/18%3A_The_Representative_Elements/18.10%3A_The_Group_6A_Elements|access-date=2020-09-20|website=Chemistry LibreTexts|language=en}}</ref> However, this discontinues starting from [[tellurium]] where the shielding is too small to produce a dip.
* Moving from the d-block to the p-block: as in the case of [[zinc]] ({{nuclide|Zn|&nbsp;}}: 9.4 eV) to [[gallium]] ({{nuclide|Ga|&nbsp;}}: 6.0 eV)
* Special case: decrease from [[lead]] ({{nuclide|Pb|&nbsp;}}: 7.42 eV) to [[bismuth]] ({{nuclide|Bi|&nbsp;}}: 7.29 eV). This cannot be attributed to size (the difference is minimal: lead has a covalent radius of 146 [[picometer|pm]] whereas [[bismuth]]'s is 148 pm<ref>{{Cite web|title=Covalent Radius for all the elements in the Periodic Table|url=https://periodictable.com/Properties/A/CovalentRadius.v.log.html|access-date=2020-09-13|website=periodictable.com}}</ref>). This is due to the spin-orbit splitting of the 6p shell (lead is removing an electron from the stabilised 6p<sub>1/2</sub> level, but bismuth is removing one from the destabilised 6p<sub>3/2</sub> level). Predicted ionization energies show a much greater decrease from [[flerovium]] to [[moscovium]], one row further down the periodic table and with much larger spin-orbit effects.
* Special case: decrease from radium ({{nuclide|Ra|&nbsp;}}: 5.27 eV) to [[actinium]] ({{nuclide|Ac|&nbsp;}}: 5.17 eV), which is a switch from an s to a d orbital. However the analogous switch from [[barium]] ({{nuclide|Ba|&nbsp;}}: 5.2 eV) to [[lanthanum]] ({{nuclide|La|&nbsp;}}: 5.6 eV) does not show a downward change.
* [[Lutetium]] ({{nuclide|Lu|&nbsp;}}) and [[lawrencium]] ({{nuclide|Lr|&nbsp;}}) both have ionization energies lower than the previous elements. In both cases the last electron added [[Electron configurations of the elements (data page)|starts a new subshell]]: 5d for Lu with electron configuration [Xe] 4f<sup>14</sup> 5d<sup>1</sup> 6s<sup>2</sup>, and 7p for Lr with configuration [Rn] 5f<sup>4</sup> 7s<sup>2</sup> 7p<sup>1</sup>. These dips in ionization energies for lutetium and especially lawrencium show that these elements belong in the d-block, and not lanthanum and actinium.<ref name="JensenLr">{{cite web|url=https://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/251.%20Lawrencium.pdf |title=Some Comments on the Position of Lawrencium in the Periodic Table |last1=Jensen |first1=W. B. |date=2015 |access-date=20 September 2015 |url-status=dead |archive-url=https://web.archive.org/web/20151223091325/https://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/251.%20Lawrencium.pdf |archive-date=23 December 2015 }}</ref>