Editing Periodic table (section)

===Group 3===
{{main|Group 3 element#Composition}}
{{Periodic table (micro)|mark=Sc,Y,Lu,Lr|title=Group&nbsp;3: Sc, Y, Lu, Lr [[Image:Yes check.svg|15px|Correct]]|caption=Correct depiction of Group 3}}
{{Periodic table (micro)|form=Sc, Y, La, Ac|mark=Sc,Y,La,Ac|title=Group&nbsp;3: Sc, Y, La, Ac [[Image:X mark.svg|15px|Incorrect]]|caption=Incorrect depiction of Group 3}}
In many periodic tables, the f-block is shifted one element to the right, so that lanthanum and actinium become d-block elements in group 3, and Ce–Lu and Th–Lr form the f-block. Thus the d-block is split into two very uneven portions. This is a holdover from early mistaken measurements of electron configurations; modern measurements are more consistent with the form with lutetium and lawrencium in group 3, and with La–Yb and Ac–No as the f-block.<ref name="Jensen1982"/><ref name=wulfsberg53/>

The 4f shell is completely filled at ytterbium, and for that reason [[Lev Landau]] and [[Evgeny Lifshitz]] in 1948 considered it incorrect to group lutetium as an f-block element.<ref name=Landau/> They did not yet take the step of removing lanthanum from the d-block as well, but [[Jun Kondō]] realized in 1963 that lanthanum's low-temperature [[superconductivity]] implied the activity of its 4f shell.<ref name=Kondo/> In 1965, David C. Hamilton linked this observation to its position in the periodic table, and argued that the f-block should be composed of the elements La–Yb and Ac–No.<ref name=Hamilton/> Since then, physical, chemical, and electronic evidence has supported this assignment.<ref name=Jensen1982/><ref name=Fluck/><ref name=wulfsberg53>Wulfsberg, p. 53: "As pointed out by W. B. Jensen, the metallurgical resemblance [to yttrium] is much stronger for lutetium than for lanthanum, so we have adopted the metallurgist's convention of listing Lu (and by extension Lr) below Sc and Y. An important additional advantage of this is that the periodic table becomes more symmetrical, and it becomes easier to predict electron configurations. E. R. Scerri points out that recent determinations of the electron configurations of most of the ''f''-block elements now are more compatible with this placement of Lu and Lr."</ref> The issue was brought to wide attention by [[William B. Jensen]] in 1982,<ref name=Jensen1982/> and the reassignment of lutetium and lawrencium to group 3 was supported by IUPAC reports dating from 1988 (when the 1–18 group numbers were recommended)<ref name="Fluck"/> and 2021.<ref name=2021IUPAC/> The variation nonetheless still exists because most textbook writers are not aware of the issue.<ref name=Jensen1982/>

A third form can sometimes be encountered in which the spaces below yttrium in group 3 are left empty, such as the table appearing on the IUPAC web site,<ref name="IUPAC-redbook" /> but this creates an inconsistency with quantum mechanics by making the f-block 15 elements wide (La–Lu and Ac–Lr) even though only 14 electrons can fit in an f-subshell.<ref name=2021IUPAC/> There is moreover some confusion in the literature on which elements are then implied to be in group 3.<ref name=2021IUPAC/><ref name=Thyssen/><ref name="JWP">{{cite journal |author=Barber, Robert C. |author2=Karol, Paul J |author3=Nakahara, Hiromichi |author4=Vardaci, Emanuele |author5=Vogt, Erich W. |title=Discovery of the elements with atomic numbers greater than or equal to 113 (IUPAC Technical Report) |doi=10.1351/PAC-REP-10-05-01 |journal=Pure Appl. Chem. |date=2011 |volume=83 |issue=7 |page=1485|doi-access=free }}</ref><ref name="Karol">{{cite journal |last1=Karol |first1=Paul J. |last2=Barber |first2=Robert C. |last3=Sherrill |first3=Bradley M. |last4=Vardaci |first4=Emanuele |last5=Yamazaki |first5=Toshimitsu |date=22 December 2015 |title=Discovery of the elements with atomic numbers Z = 113, 115 and 117 (IUPAC Technical Report) |journal=Pure Appl. Chem. |volume=88 |issue=1–2 |pages=139–153 |doi=10.1515/pac-2015-0502|doi-access=free }}</ref><ref>{{cite journal |last1=Pyykkö |first1=Pekka |date=2019 |title=An essay on periodic tables |url=http://www.chem.helsinki.fi/~pyykko/pekka/No330b.pdf |journal=Pure and Applied Chemistry |volume=91 |issue=12 |pages=1959–1967 |doi=10.1515/pac-2019-0801 |s2cid=203944816 |access-date=27 November 2022}}</ref> While the 2021 IUPAC report noted that 15-element-wide f-blocks are supported by some practitioners of a specialized branch of [[relativistic quantum mechanics]] focusing on the properties of [[superheavy element]]s, the project's opinion was that such interest-dependent concerns should not have any bearing on how the periodic table is presented to "the general chemical and scientific community".<ref name=2021IUPAC/> Other authors focusing on superheavy elements since clarified that the "15th entry of the f-block represents the first slot of the d-block which is left vacant to indicate the place of the f-block inserts", which would imply that this form still has lutetium and lawrencium (the 15th entries in question) as d-block elements in group 3.<ref name=smits/> Indeed, when IUPAC publications expand the table to 32 columns, they make this clear and place lutetium and lawrencium under yttrium in group 3.<ref>{{cite journal |last1=Leigh |first1=G. Jeffrey |date=2009 |title=Periodic Tables and IUPAC |url=https://publications.iupac.org/ci/2009/3101/1_leigh.html |journal=Chemistry International |volume=31 |issue=1 |pages=4–6 |doi=10.1515/ci.2009.31.1.4 |access-date=8 January 2024}}</ref><ref>{{cite book |editor-last=Leigh |editor-first=G. Jeffrey |date=1990 |title=Nomenclature of inorganic chemistry : recommendations 1990 |url=https://archive.org/details/nomenclatureofin0000unse/page/282/mode/2up |location= |publisher=Blackwell Scientific Publications |page=283 |isbn=0-632-02319-8}}</ref>

Several arguments in favour of Sc-Y-La-Ac can be encountered in the literature,<ref>{{cite journal |last1= Vernon|first1= R|date= 2021|title=The location and composition of Group 3 of the periodic table|journal=Foundations of Chemistry |volume= 23|issue= 2|pages= 155–197|doi=10.1007/s10698-020-09384-2|s2cid= 254501533|doi-access= free}}</ref><ref>{{cite journal |last1=Cotton |first1=SA |last2=Raithby |first2=BR |last3=Shield |first3=A|date= 2022|title= A comparison of the structural chemistry of scandium, yttrium, lanthanum and lutetium: A contribution to the group 3 debate |journal= Coordination Chemistry Reviews |volume=455 |issue= |page= 214366 |doi= 10.1016/j.ccr.2021.214366|s2cid=245712597 |url=https://purehost.bath.ac.uk/ws/files/227604162/CCR_SC_Y_Ln_Manuscript_accepted_131221.pdf }}</ref> but they have been challenged as being logically inconsistent.<ref name="Jensen-2015" /><ref name=Scerri2009/><ref name=Chemey/> For example, it has been argued that lanthanum and actinium cannot be f-block elements because as individual gas-phase atoms, they have not begun to fill the f-subshells.<ref name=Lavelle>{{cite journal |last1=Lavelle |first1=Laurence |date=2008 |title=Lanthanum (La) and Actinium (Ac) Should Remain in the d-block |journal=Journal of Chemical Education |volume=85 |issue=11 |pages=1482–1483 |doi=10.1021/ed085p1482|bibcode=2008JChEd..85.1482L |doi-access=free }}</ref> But the same is true of thorium which is never disputed as an f-block element,<ref name=2021IUPAC/><ref name=Jensen1982/> and this argument overlooks the problem on the other end: that the f-shells complete filling at ytterbium and nobelium, matching the Sc-Y-Lu-Lr form, and not at lutetium and lawrencium as the Sc-Y-La-Ac form would have it.<ref name=johnson>{{cite book |last=Johnson |first=David |date=1984 |title=The Periodic Law |url=https://www.rsc.org/images/23_The_Periodic_Law_tcm18-30005.pdf |location= |publisher=The Royal Society of Chemistry |page= |isbn=0-85186-428-7}}</ref> Not only are such exceptional configurations in the minority,<ref name=johnson/> but they have also in any case never been considered as relevant for positioning any other elements on the periodic table: in gaseous atoms, the d-shells complete their filling at copper, palladium, and gold, but it is universally accepted by chemists that these configurations are exceptional and that the d-block really ends in accordance with the Madelung rule at zinc, cadmium, and mercury.<ref name="Thyssen"/> The relevant fact for placement<ref name=Jensen2009/><ref name=JensenLr/> is that lanthanum and actinium (like thorium) have valence f&nbsp;orbitals that can become occupied in chemical environments, whereas lutetium and lawrencium do not:<ref name=jensenlaw/><ref name="Wittig">{{cite book |last=Wittig |first=Jörg |editor=H. J. Queisser |date=1973 |title=Festkörper Probleme: Plenary Lectures of the Divisions Semiconductor Physics, Surface Physics, Low Temperature Physics, High Polymers, Thermodynamics and Statistical Mechanics, of the German Physical Society, Münster, March 19–24, 1973 |chapter=The pressure variable in solid state physics: What about 4f-band superconductors? |series=Advances in Solid State Physics |volume=13 |location=Berlin, Heidelberg |publisher=Springer |pages=375–396 |isbn=978-3-528-08019-8 |doi=10.1007/BFb0108579}}</ref><ref name=XuPyykko/> their f-shells are in the core, and cannot be used for chemical reactions.<ref name=Cp3Ln/><ref name=wulfsberg26/> Thus the relationship between yttrium and lanthanum is only a secondary relationship between elements with the same number of valence electrons but different kinds of valence orbitals, such as that between chromium and uranium; whereas the relationship between yttrium and lutetium is primary, sharing both valence electron count and valence orbital type.<ref name=jensenlaw/>