Editing Nickel (section)

===Atomic and physical properties===
[[File:Ni@CNT2.jpg|thumb|left|[[Transmission electron microscopy|Electron micrograph]] of a Ni nanocrystal inside a single wall [[carbon nanotube]]; scale bar 5&nbsp;nm<ref>{{cite journal|doi=10.1038/srep15033|pmid=26459370|pmc=4602218|title=Nickel clusters embedded in carbon nanotubes as high performance magnets|journal=Scientific Reports|volume=5|page=15033|date=2015|display-authors=4|last1=Shiozawa|first1=Hidetsugu|last2=Briones-Leon|first2=Antonio|last3=Domanov|first3=Oleg|last4=Zechner|first4=Georg|last5=Sato|first5=Yuta|last6=Suenaga|first6=Kazu|last7=Saito|first7=Takeshi|last8=Eisterer|first8=Michael|last9=Weschke|first9=Eugen|last10=Lang|first10=Wolfgang|last11=Peterlik|first11=Herwig|last12=Pichler|first12=Thomas|bibcode=2015NatSR...515033S}}</ref>]]
Nickel is a silvery-white metal with a slight golden tinge that takes a high polish. It is one of only four elements that are [[Ferromagnetism|ferromagnetic]] at or near room temperature; the others are iron, [[cobalt]] and [[gadolinium]]. Its [[Curie temperature]] is {{convert|355|°C|°F|}}, meaning that bulk nickel is non-magnetic above this temperature.<ref>{{cite book |author=Kittel, Charles|title=[[Introduction to Solid State Physics]] |publisher=Wiley |date=1996 |page=449 |isbn=978-0-471-14286-7}}</ref><ref name="CoeySkumryev1999" /> The unit cell of nickel is a [[Cubic crystal system|face-centered cube]]; it has lattice parameter of 0.352&nbsp;nm, giving an [[atomic radius]] of 0.124&nbsp;nm. This crystal structure is stable to pressures of at least 70&nbsp;GPa. Nickel is hard, malleable and [[Ductility|ductile]], and has a relatively high [[Electrical resistivity and conductivity|electrical]] and [[thermal conductivity]] for transition metals.<ref name="crc" /> The high [[compressive strength]] of 34 GPa, predicted for ideal crystals, is never obtained in the real bulk material due to formation and movement of [[dislocation]]s. However, it has been reached in Ni [[nanoparticle]]s.<ref>{{cite journal|doi=10.1038/s41467-018-06575-6|pmid=30291239|pmc=6173750|title=Nickel nanoparticles set a new record of strength|journal=Nature Communications|volume=9|issue=1|pages=4102|year=2018|last1=Sharma|first1=A.|last2=Hickman|first2=J.|last3=Gazit|first3=N.|last4=Rabkin|first4=E.|last5=Mishin|first5=Y.|bibcode=2018NatCo...9.4102S}}</ref>

====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>