Editing Transition metal (section)

==Definition and classification==
The 2011 [[International Union of Pure and Applied Chemistry name|IUPAC]] ''Principles of Chemical Nomenclature'' describe a "transition metal" as any element in groups 3 to 12 on the [[periodic table]].<ref>{{cite book |editor-last=Leigh |editor-first=G. J. |date=2011 |title=Principles of Chemical Nomenclature |url=https://iupac.org/wp-content/uploads/2021/12/Principles_Leigh2011-compressed.pdf |location= |publisher=The Royal Society of Chemistry |page=9 |isbn=978-1-84973-007-5}}</ref> This corresponds exactly to the [[d-block]] elements, and many scientists use this definition.<ref>{{cite book |last1 = Petrucci |first1 = Ralph H. |last2 = Harwood |first2 = William S. |last3 = Herring |first3 = F. Geoffrey |date=2002 |title = General chemistry: principles and modern applications |url = https://archive.org/details/generalchemistry00hill |url-access = registration |edition=8th |location=Upper Saddle River, N.J |publisher=Prentice Hall |isbn = 978-0-13-014329-7 |lccn=2001032331 |oclc=46872308 |pages=[https://archive.org/details/generalchemistry00hill/page/341 341–342]}}</ref><ref>Housecroft, C.&nbsp;E. and Sharpe, A.&nbsp;G. (2005) ''Inorganic Chemistry'', 2nd ed, Pearson Prentice-Hall, pp. 20–21.</ref> In actual practice, the [[f-block]] [[lanthanide]] and [[actinide]] series are called "inner transition metals". The 2005 ''[[IUPAC Red Book|Red Book]]'' allows for the group 12 elements to be excluded, but not the 2011 ''Principles''.<ref name=RedBook>{{cite book
 |editor-last1=Connelly
 |editor-first1=N.G.
 |editor-last2=Damhus
 |editor-first2=T.
 |editor-last3=Hartshorn
 |editor-first3=R.M.
 |editor-last4=Hutton
 |editor-first4=A.T.
 |year=2005
 |url=http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf
 |title=Nomenclature of Inorganic Chemistry
 |publisher=[[Royal Society of Chemistry|RSC]]–[[International Union of Pure and Applied Chemistry|IUPAC]]
 |isbn=0-85404-438-8
}}</ref>

The IUPAC ''[[IUPAC Gold Book|Gold Book]]''<ref>{{GoldBookRef|file=T06456|title=transition element}}</ref> defines a transition metal as "an [[chemical element|element]] whose atom has a partially filled [[Electron shell|d]] sub-shell, or which can give rise to [[cation]]s with an incomplete d sub-shell", but this definition is taken from an old edition of the ''Red Book'' and is no longer present in the current edition.<ref name=RedBook/>

In the d-block, the atoms of the elements have between zero and ten d electrons.
{| class=wikitable style="margin:0.5em 1em 0.5em 0; text-align:center; background:{{element color|d-block}}; border: 1px solid {{element color|table border}}; padding:2px; font-size: 85%;"
|-
|+ style="background-color:{{element color|table title}}" | Transition metals in the d-block
|- style="background:{{element color|table header}}" | 
! [[Group (periodic table)|Group]]
! [[Group 3 element|3]]
! [[Group 4 element|4]]
! [[Group 5 element|5]]
! [[Group 6 element|6]]
! [[Group 7 element|7]]
! [[Group 8 element|8]]
! [[Group 9 element|9]]
! [[Group 10 element|10]]
! [[Group 11 element|11]]
! [[Group 12 element|12]]
|-
!style="background:{{element color|table colheader}}"| [[Period 4 element|Period 4]]
| <sub>21</sub>[[Scandium|Sc]]
| <sub>22</sub>[[Titanium|Ti]]
| <sub>23</sub>[[Vanadium|V]]
| <sub>24</sub>[[Chromium|Cr]]
| <sub>25</sub>[[Manganese|Mn]]
| <sub>26</sub>[[Iron|Fe]]
| <sub>27</sub>[[Cobalt|Co]]
| <sub>28</sub>[[Nickel|Ni]]
| <sub>29</sub>[[Copper|Cu]]
| <sub>30</sub>[[Zinc|Zn]]
|-
!style="background:{{element color|table colheader}}"| [[Period 5 element|5]]
| <sub>39</sub>[[Yttrium|Y]]
| <sub>40</sub>[[Zirconium|Zr]]
| <sub>41</sub>[[Niobium|Nb]]
| <sub>42</sub>[[Molybdenum|Mo]]
| <sub>43</sub>[[Technetium|Tc]]
| <sub>44</sub>[[Ruthenium|Ru]]
| <sub>45</sub>[[Rhodium|Rh]]
| <sub>46</sub>[[Palladium|Pd]]
| <sub>47</sub>[[Silver|Ag]]
| <sub>48</sub>[[Cadmium|Cd]]
|-
!style="background:{{element color|table colheader}}"| [[Period 6 element|6]]
| <sub>71</sub>[[Lutetium|Lu]]
| <sub>72</sub>[[Hafnium|Hf]]
| <sub>73</sub>[[Tantalum|Ta]]
| <sub>74</sub>[[Tungsten|W]]
| <sub>75</sub>[[Rhenium|Re]]
| <sub>76</sub>[[Osmium|Os]]
| <sub>77</sub>[[Iridium|Ir]]
| <sub>78</sub>[[Platinum|Pt]]
| <sub>79</sub>[[Gold|Au]]
| <sub>80</sub>[[Mercury (element)|Hg]]
|-
!style="background:{{element color|table colheader}}"| [[Period 7 element|7]]
| <sub>103</sub>[[Lawrencium|Lr]]
| <sub>104</sub>[[Rutherfordium|Rf]]
| <sub>105</sub>[[Dubnium|Db]]
| <sub>106</sub>[[Seaborgium|Sg]]
| <sub>107</sub>[[Bohrium|Bh]]
| <sub>108</sub>[[Hassium|Hs]]
| <sub>109</sub>[[Meitnerium|Mt]]
| <sub>110</sub>[[Darmstadtium|Ds]]
| <sub>111</sub>[[Roentgenium|Rg]]
| <sub>112</sub>[[Copernicium|Cn]]
|}

Published texts and periodic tables show [[Group 3 element#Composition|variation regarding the heavier members of group 3]].<ref name="PTSS">{{cite book | last=Scerri | first=Eric R. | title=The Periodic Table: Its Story and Its Significance | publication-place=New York, NY | date=2020 | isbn=978-0-19-091436-3 | oclc=1096234740}}</ref> The common placement of [[lanthanum]] and [[actinium]] in these positions is not supported by physical, chemical, and electronic [[Scientific evidence|evidence]],<ref>{{cite book
 |author=[[Lev Landau|L. D. Landau]], [[Evgeny Lifshitz|E. M. Lifshitz]]
 |year=1958
 |title=Quantum Mechanics: Non-Relativistic Theory
 |edition=1st |volume=3
 |publisher=[[Pergamon Press]]
 |pages=256–7
}}</ref><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>{{cite book |last=Matthias |first=B. T. |date=1969 |editor-last=Wallace |editor-first=P. R. |title=Superconductivity |publisher=Gordon and Breach |pages=225–294 <!--precise quote calling it a mistake is on pp. 247–9--> |chapter=Systematics of Super Conductivity |isbn=9780677138107 |volume=1}}</ref> which overwhelmingly favour putting [[lutetium]] and [[lawrencium]] in those places.<ref name="Jensen1982">{{cite journal |title=The Positions of Lanthanum (Actinium) and Lutetium (Lawrencium) in the Periodic Table |author=William B. Jensen |journal=J. Chem. Educ. |year=1982 |volume=59 |issue = 8|pages=634–636 |doi=10.1021/ed059p634|bibcode=1982JChEd..59..634J }}</ref><ref name="Jensen2015">{{cite journal |last1=Jensen |first1=William B. |date=2015 |title=The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table: an update |url=https://link.springer.com/article/10.1007/s10698-015-9216-1 |journal=Foundations of Chemistry |volume=17 |issue= |pages=23–31 |doi=10.1007/s10698-015-9216-1 |s2cid=98624395 |access-date=28 January 2021 |archive-date=30 January 2021 |archive-url=https://web.archive.org/web/20210130011116/https://link.springer.com/article/10.1007/s10698-015-9216-1 |url-status=live }}</ref> Some authors prefer to leave the spaces below [[yttrium]] blank as a third option, but there is confusion on whether this format implies that group 3 contains only [[scandium]] and yttrium, or if it also contains all the lanthanides and actinides;<ref name=2021IUPAC/><ref name="Thyssen">{{cite book|last1=Thyssen|first1=P.|last2=Binnemans|first2=K.|editor1-last=Gschneidner|editor1-first= K. A. Jr.|editor2-last=Bünzli|editor2-first=J-C.G|editor3-last=Vecharsky|editor3-first=Bünzli|date=2011|chapter=Accommodation of the Rare Earths in the Periodic Table: A Historical Analysis|title=Handbook on the Physics and Chemistry of Rare Earths|publisher=Elsevier|location=Amsterdam|volume=41|pages=1–94|isbn=978-0-444-53590-0|doi=10.1016/B978-0-444-53590-0.00001-7}}</ref><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> additionally, it creates a 15-element-wide f-block, when [[quantum mechanics]] dictates that the f-block should only be 14 elements wide.<ref name=2021IUPAC/> The form with lutetium and lawrencium in group 3 is supported by a 1988 [[IUPAC]] report on physical, chemical, and electronic grounds,<ref name="Fluck">{{cite journal |last1=Fluck |first1=E. |year=1988 |title=New Notations in the Periodic Table |journal=[[Pure and Applied Chemistry|Pure Appl. Chem.]] |volume=60 |pages=431–436|doi=10.1351/pac198860030431 |url=https://www.iupac.org/publications/pac/1988/pdf/6003x0431.pdf |access-date=24 March 2012 |issue=3 |s2cid=96704008 |url-status=live |archive-url=https://web.archive.org/web/20120325152951/https://www.iupac.org/publications/pac/1988/pdf/6003x0431.pdf |archive-date=25 March 2012}}</ref> and again by a 2021 IUPAC preliminary report as it is the only form that allows simultaneous (1) preservation of the sequence of increasing atomic numbers, (2) a 14-element-wide f-block, and (3) avoidance of the split in the d-block.<ref name="2021IUPAC">{{cite journal |last1=Scerri |first1=Eric |date=18 January 2021 |title=Provisional Report on Discussions on Group 3 of the Periodic Table |url=https://iupac.org/wp-content/uploads/2021/04/ChemInt_Jan2021_PP.pdf |journal=Chemistry International |volume=43 |issue=1 |pages=31–34 |doi=10.1515/ci-2021-0115 |s2cid=231694898 |access-date=9 April 2021 |archive-date=13 April 2021 |archive-url=https://web.archive.org/web/20210413150110/https://iupac.org/wp-content/uploads/2021/04/ChemInt_Jan2021_PP.pdf |url-status=live }}</ref> Argumentation can still be found in the contemporary literature purporting to defend the form with lanthanum and actinium in group 3, but many authors consider it to be logically inconsistent (a particular point of contention being the differing treatment of [[actinium]] and [[thorium]], which both can use 5f as a [[Valence (chemistry)|valence]] [[Orbital hybridisation|orbital]] but have no 5f occupancy as single atoms);<ref name=Jensen2015/><ref name=Scerri2009>{{cite journal |last1=Scerri |first1=Eric |date=2009 |title=Which Elements Belong in Group 3? |url=https://pubs.acs.org/doi/pdf/10.1021/ed086p1188 |journal=Journal of Chemical Education |volume=86 |issue=10 |pages=1188 |doi=10.1021/ed086p1188 |bibcode=2009JChEd..86.1188S |access-date=1 January 2023}}</ref><ref name=Chemey>{{cite journal |last1=Chemey |first1=Alexander T. |last2=Albrecht-Schmitt |first2=Thomas E. |date=2019 |title=Evolution of the periodic table through the synthesis of new elements |url= |journal=Radiochimica Acta |volume=107 |issue=9–11 |pages=771–801 |doi=10.1515/ract-2018-3082 |s2cid=104470619 |access-date=}}</ref> the majority of investigators considering the problem agree with the updated form with lutetium and lawrencium.<ref name=Jensen2015/>

The group 12 elements [[zinc]], [[cadmium]], and [[mercury (element)|mercury]] are sometimes excluded from the transition metals.<ref name=Jensen>{{cite journal |journal = Journal of Chemical Education |volume = 80 |issue = 8 |year = 2003 |url = http://www.uv.es/~borrasj/ingenieria_web/temas/tema_1/lecturas_comp/p952.pdf |title = The Place of Zinc, Cadmium, and Mercury in the Periodic Table |first = William B. |last = Jensen |pages=952–961 |doi = 10.1021/ed080p952 |bibcode = 2003JChEd..80..952J }}</ref> This is because they have the [[electronic configuration]] [&nbsp;]d<sup>10</sup>s<sup>2</sup>, where the d shell is complete,<ref>Cotton, F. Albert; Wilkinson, G.; Murillo, C. A. (1999). ''Advanced Inorganic Chemistry'' (6th ed.). New York: Wiley, {{ISBN|978-0-471-19957-1}}.</ref> and they still have a complete d shell in all their known [[oxidation state]]s. The group 12 elements Zn, Cd and Hg may therefore, under certain criteria, be classed as [[post-transition metal]]s in this case. However, it is often convenient to include these elements in a discussion of the transition elements. For example, when discussing the [[Crystal field theory#Crystal field stabilization energy|crystal field stabilization energy]] of first-row transition elements, it is convenient to also include the elements [[calcium]] and zinc, as both {{chem|Ca|2+}} and {{chem|Zn|2+}} have a value of zero, against which the value for other transition metal ions may be compared. Another example occurs in the [[Irving–Williams series]] of stability constants of complexes. Moreover, Zn, Cd, and Hg can use their d orbitals for [[Bonding (chemistry)|bonding]] even though they are not known in oxidation states that would formally require breaking open the d-subshell, which sets them apart from the p-block elements.<ref>{{cite journal |last1=Tossell |first1=J.A. |date=1 November 1977 |title=Theoretical studies of valence orbital binding energies in solid zinc sulfide, zinc oxide, and zinc fluoride |journal=Inorganic Chemistry |volume=16 |issue=11 |pages=2944–2949 |doi=10.1021/ic50177a056}}</ref><ref>{{cite journal |last1=Farberovich |first1=O. V. |last2=Kurganskii |first2=S. I. |last3=Domashevskaya |first3=E. P. |date=1980 |title=Problems of the OPW Method. II. Calculation of the Band Structure of ZnS and CdS |url= |journal=Physica Status Solidi B |volume=97 |issue=2 |pages=631–640 |doi=10.1002/pssb.2220970230 |bibcode=1980PSSBR..97..631F |access-date=}}</ref><ref>{{cite journal |last1=Singh |first1=Prabhakar P. |date=1994 |title=Relativistic effects in mercury: Atom, clusters, and bulk |url= |journal=Physical Review B |volume=49 |issue=7 |pages=4954–4958 |doi=10.1103/PhysRevB.49.4954 |pmid=10011429 |bibcode=1994PhRvB..49.4954S |access-date=}}</ref>

The 2007 (though disputed and so far not reproduced independently) synthesis of [[mercury(IV) fluoride]] ({{chem|HgF|4}}) has been taken by some to reinforce the view that the group 12 elements should be considered transition metals,<ref>{{cite journal |title=Mercury Is a Transition Metal: The First Experimental Evidence for HgF<sub>4</sub> |journal=Angew. Chem. Int. Ed. |year=2007 |volume=46 |issue=44 |pages=8371–8375 |doi=10.1002/anie.200703710 |pmid=17899620 |last1=Wang |first1=Xuefang |last2=Andrews |first2=Lester |last3=Riedel |first3=Sebastian |last4=Kaupp |first4=Martin}}</ref> but some authors still consider this compound to be exceptional.<ref>{{cite journal |title=Is Mercury Now a Transition Element? |author=Jensen, William B.  |journal=J. Chem. Educ. |year=2008 |volume=85 |pages=1182–1183 |doi=10.1021/ed085p1182|bibcode = 2008JChEd..85.1182J |issue=9 |doi-access=free }}</ref> [[Copernicium]] is expected to be able to use its d electrons for chemistry as its 6d [[Electron shell|subshell]] is destabilised by strong [[relativistic quantum chemistry|relativistic effects]] due to its very high atomic number, and as such is expected to have transition-metal-like behaviour and show higher oxidation states than +2 (which are not definitely known for the lighter group 12 elements). Even in bare dications, Cn<sup>2+</sup> is predicted to be 6d<sup>8</sup>7s<sup>2</sup>, unlike Hg<sup>2+</sup> which is 5d<sup>10</sup>6s<sup>0</sup>.

Although [[meitnerium]], [[darmstadtium]], and [[roentgenium]] are within the d-block and are expected to behave as transition metals analogous to their lighter [[Congener (chemistry)|congeners]] [[iridium]], [[platinum]], and [[gold]], this has not yet been experimentally confirmed. Whether [[copernicium]] behaves more like [[mercury (element)|mercury]] or has properties more similar to those of the [[noble gas]] [[radon]] is not clear. Relative inertness of Cn would come from the relativistically expanded 7s–7p<sub>1/2</sub> energy gap, which is already adumbrated in the 6s–6p<sub>1/2</sub> gap for Hg, weakening metallic bonding and causing its well-known low melting and boiling points.

Transition metals with lower or higher group numbers are described as 'earlier' or 'later', respectively.  When described in a two-way classification scheme, early transition metals are on the left side of the d-block from group 3 to group 7. Late transition metals are on the right side of the d-block, from group 8 to 11 (or 12, if they are counted as transition metals).  In an alternative three-way scheme, groups 3, 4, and 5 are classified as early transition metals, 6, 7, and 8 are classified as middle transition metals, and 9, 10, and 11 (and sometimes group 12) are classified as late transition metals. 

The heavy group 2 elements [[calcium]], [[strontium]], and [[barium]] do not have filled d-orbitals as single atoms, but are known to have d-orbital bonding participation in some [[Chemical compound|compounds]], and for that reason have been called "honorary" transition metals.<ref>{{cite journal |last1=Fernández |first1=Israel |last2=Holzmann |first2=Nicole |last3=Frenking |first3=Gernot |date=2020 |title=The Valence Orbitals of the Alkaline-Earth Atoms |journal=Chemistry: A European Journal |volume=26 |issue=62 |pages=14194–14210 |doi=10.1002/chem.202002986 |pmid=32666598 |pmc=7702052 |s2cid=220529532 |doi-access=free }}</ref> The same is likely true of [[radium]].<ref>{{cite journal |last1=Pyykkö |first1=Pekka |last2=Desclaux |first2=Jean-Paul |date=1979 |title=Relativity and the Periodic System of Elements |journal=Accounts of Chemical Research |volume=12 |issue=8 |pages=276–281 |doi=10.1021/ar50140a002 |pmid= |pmc= |s2cid= |doi-access= }}</ref>

The f-block elements La–Yb and Ac–No have chemical activity of the (n−1)d shell, but importantly also have chemical activity of the (n−2)f shell that is absent in d-block elements. Hence they are often treated separately as inner transition elements.