Editing Nickel (section)

====Electron configuration dispute====
Nickel has two atomic [[electron configuration]]s, [Ar] 3d{{sup|8}} 4s{{sup|2}} and [Ar] 3d{{sup|9}} 4s{{sup|1}}, which are very close in energy; [Ar] denotes the complete [[argon]] core structure. There is some disagreement on which configuration has the lower energy.<ref name="Scerri" /> Chemistry textbooks quote nickel's electron configuration as [Ar] 4s{{sup|2}} 3d{{sup|8}},<ref>Miessler, G.L. and Tarr, D.A. (1999) ''Inorganic Chemistry'' 2nd ed., Prentice–Hall. p. 38. {{ISBN|0138418918}}.</ref> also written [Ar] 3d{{sup|8}} 4s{{sup|2}}.<ref>Petrucci, R.H. et al. (2002) ''General Chemistry'' 8th ed., Prentice–Hall. p. 950. {{ISBN|0130143294}}.</ref> This configuration agrees with the [[Madelung rule|Madelung energy ordering rule]], which predicts that 4s is filled before 3d. It is supported by the experimental fact that the lowest energy state of the nickel atom is a 3d{{sup|8}} 4s{{sup|2}} energy level, specifically the 3d{{sup|8}}({{sup|3}}F) 4s{{sup|2}} {{sup|3}}F, ''J''&nbsp;=&nbsp;4 level.<ref name="JPCRD">{{cite web |last1=Corliss |first1=Charles |last2=Sugar |first2=Jack |title=Energy levels of nickel, Ni I through Ni XXVIII |page=200 |url=https://srd.nist.gov/jpcrdreprint/1.555638.pdf |publisher=Journal of Physical and Chemical Reference Data |access-date=5 March 2023 |date=15 October 2009 |quote=In this table Ni I = neutral Ni atom, Ni II = Ni+ etc.}}</ref><ref name="NIST">[http://physics.nist.gov/PhysRefData/ASD/levels_form.html NIST Atomic Spectrum Database] {{Webarchive|url=https://web.archive.org/web/20110320190125/http://physics.nist.gov/PhysRefData/ASD/levels_form.html |date=March 20, 2011 }} To read the nickel atom levels, type "Ni 0" or "Ni I" in the Spectrum box and click on Retrieve data.</ref>

However, each of these two configurations splits into several energy levels due to [[fine structure]],<ref name="JPCRD"/><ref name="NIST" /> and the two sets of energy levels overlap. The average energy of states with [Ar] 3d{{sup|9}} 4s{{sup|1}} is actually lower than the average energy of states with [Ar] 3d{{sup|8}} 4s{{sup|2}}. Therefore, the research literature on atomic calculations quotes the ground state configuration as [Ar] 3d{{sup|9}} 4s{{sup|1}}.<ref name="Scerri">{{cite book |url=https://archive.org/details/periodictableits0000scer |url-access=registration |pages=[https://archive.org/details/periodictableits0000scer/page/239 239]–240 |title=The periodic table: its story and its significance |author=Scerri, Eric R. |author-link = Eric Scerri |publisher=Oxford University Press|date=2007 |isbn=978-0-19-530573-9}}</ref>