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Periodic table
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== Classification of elements == [[File:Simple Periodic Table Chart-en.svg|512px|thumb|right|A periodic table colour-coded to show some commonly used sets of similar elements. The categories and their boundaries differ somewhat between sources.<ref name="ACS">{{cite web |url=https://www.acs.org/content/acs/en/education/whatischemistry/periodictable.html |title=Periodic Table of Chemical Elements |date=2021 |website=www.acs.org |publisher=[[American Chemical Society]] |access-date=27 March 2021 |archive-date=3 February 2021 |archive-url=https://web.archive.org/web/20210203123434/https://www.acs.org/content/acs/en/education/whatischemistry/periodictable.html |url-status=live }}</ref> Lutetium and lawrencium in group 3 are also transition metals.<ref name=jensenlaw/>{{col-begin}}{{col-break}}{{Legend inline|ff9d9d}} [[Alkali metals]]<br />{{Legend inline|ffdead}} [[Alkaline earth metals]]<br />{{Legend inline|ffbfff}} [[Lanthanides]]<br />{{Legend inline|ff99cc}} [[Actinides]]<br />{{Legend inline|ffc0c0}} [[Transition metals]]{{col-break}}{{Legend inline|cccccc}} [[Other metals]]<br />{{Legend inline|cccc99}} [[Metalloids]]<br />{{Legend inline|a0ffa0}} [[Other nonmetal]]s<br />{{Legend inline|ffff99}} [[Halogens]]<br />{{Legend inline|c0ffff}} [[Noble gases]]{{col-end}}]] Many terms have been used in the literature to describe sets of elements that behave similarly. The group names ''alkali metal'', ''alkaline earth metal'', ''triel'', ''tetrel'', ''pnictogen'', ''chalcogen'', ''halogen'', and ''noble gas'' are acknowledged by IUPAC; the other groups can be referred to by their number, or by their first element (e.g., group 6 is the chromium group).<ref name="IUPAC" /><ref>{{cite journal |last1=Fernelius |first1=W. C. |last2=Loening |first2=Kurt |last3=Adams |first3=Roy M. |date=1971 |title=Names of groups and elements |url= |journal=Journal of Chemical Education |volume=48 |issue=11 |pages=730–731 |doi=10.1021/ed048p730 |bibcode=1971JChEd..48..730F }}</ref> Some divide the p-block elements from groups 13 to 16 by metallicity,<ref name="EB" /><ref name="ACS" /> although there is neither an IUPAC definition nor a precise consensus on exactly which elements should be considered metals, nonmetals, or semi-metals (sometimes called metalloids).<ref name="EB" /><ref name="ACS" /><ref name="IUPAC" /> Neither is there a consensus on what the metals succeeding the transition metals ought to be called, with ''[[post-transition metal]]'' and ''poor metal'' being among the possibilities having been used. Some advanced monographs exclude the elements of group 12 from the transition metals on the grounds of their sometimes quite different chemical properties, but this is not a universal practice<ref>{{cite journal|last1=Jensen |first1=William B. |year=2003 |title=The Place of Zinc, Cadmium, and Mercury in the Periodic Table |journal=Journal of Chemical Education |volume=80 |issue=8 |pages=952–961 |doi=10.1021/ed080p952 |bibcode=2003JChEd..80..952J |url=https://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/091.%20Zn-Cd-Hg.pdf |access-date=6 May 2012 |archive-url=https://web.archive.org/web/20100611152417/https://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/091.%20Zn-Cd-Hg.pdf |archive-date=11 June 2010 }}</ref> and IUPAC does not presently mention it as allowable in its ''Principles of Chemical Nomenclature''.<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> The ''lanthanides'' are considered to be the elements La–Lu, which are all very similar to each other: historically they included only Ce–Lu, but lanthanum became included by common usage.<ref name=IUPAC/> The ''[[rare earth element]]s'' (or rare earth metals) add scandium and yttrium to the lanthanides.<ref name="IUPAC" /> Analogously, the ''actinides'' are considered to be the elements Ac–Lr (historically Th–Lr),<ref name="IUPAC" /> although variation of properties in this set is much greater than within the lanthanides.<ref name="Jorgensen" /> IUPAC recommends the names ''lanthanoids'' and ''actinoids'' to avoid ambiguity, as the -ide suffix typically denotes a negative ion; however ''lanthanides'' and ''actinides'' remain common.<ref name="IUPAC" /> With the increasing recognition of lutetium and lawrencium as d-block elements, some authors began to define the lanthanides as La–Yb and the actinides as Ac–No, matching the f-block.<ref name=KW/><ref name=Jensen1982/><ref>{{cite web |url=https://www.webelements.com/ |title=WebElements |last=Winter |first=Mark |date=1993–2022 |website= |publisher=The University of Sheffield and WebElements Ltd, UK |access-date=5 December 2022 |quote=}}</ref><ref>{{cite book |last=Cowan |first=Robert D. |date=1981 |title=The Theory of Atomic Structure and Spectra |url= |location= |publisher=University of California Press |page=598 |isbn=978-0-520-90615-0}}</ref><ref>{{cite journal |last1=Villar |first1=G. E. |date=1966 |title=A suggested modification to the periodic chart |url= |journal=Journal of Inorganic and Nuclear Chemistry |volume=28 |issue=1 |pages=25–29 |doi=10.1016/0022-1902(66)80224-5 }}</ref><ref name=sacotton>{{cite journal |last1=Cotton |first1=S. A. |date=1996 |title=After the actinides, then what? |url= |journal=Chemical Society Reviews |volume=25 |issue=3 |pages=219–227 |doi=10.1039/CS9962500219 |access-date=}}</ref> The ''transactinides'' or ''[[superheavy element]]s'' are the short-lived elements beyond the actinides, starting at lawrencium or rutherfordium (depending on where the actinides are taken to end).<ref name=sacotton/><ref name=Neve>{{cite journal |last1=Neve |first1=Francesco |date=2022 |title=Chemistry of superheavy transition metals |url= |journal=Journal of Coordination Chemistry |volume=75 |issue=17–18 |pages=2287–2307 |doi=10.1080/00958972.2022.2084394 |s2cid=254097024 }}</ref><ref name=Mingos>{{cite book |last=Mingos |first=Michael |author-link=Michael Mingos |date=1998 |title=Essential Trends in Inorganic Chemistry |url= |location= |publisher=Oxford University Press |page=387 |isbn=978-0-19-850109-1}}<!--uses "transactinide" rather than "superheavy--></ref><ref>{{cite web |url=https://science.osti.gov/-/media/np/nsac/pdf/202310/October-4-LRP-Report.pdf |archive-url=https://web.archive.org/web/20231005134013/https://science.osti.gov/-/media/np/nsac/pdf/202310/October-4-LRP-Report.pdf |archive-date=5 October 2023 |title=A New Era of Discovery: the 2023 Long Range Plan for Nuclear Science |publisher=U.S. Department of Energy |date=October 2023 |via=OSTI |access-date=20 October 2023 |quote=Superheavy elements (''Z'' > 102) are teetering at the limits of mass and charge.}}</ref><ref>{{cite arXiv|last=Kragh|first=Helge|author-link=|date=2017|title=The search for superheavy elements: Historical and philosophical perspectives|eprint=1708.04064|class=physics.hist-ph}}</ref> Many more categorizations exist and are used according to certain disciplines. In astrophysics, a metal is defined as any element with atomic number greater than 2, i.e. anything except hydrogen and helium.<ref>{{cite web |url=https://icc.dur.ac.uk/~tt/Lectures/Galaxies/TeX/lec/node27.html |title=Metallicity of stars |last=Theuns |first=Tom |website=icc.dur.ac.uk |publisher=Durham University |access-date=27 March 2021 |archive-date=27 September 2021 |archive-url=https://web.archive.org/web/20210927160927/https://icc.dur.ac.uk/~tt/Lectures/Galaxies/TeX/lec/node27.html |url-status=live }}</ref> The term "semimetal" has a different definition in physics than it does in chemistry: bismuth is a semimetal by physical definitions, but chemists generally consider it a metal.<ref>{{cite book |first=Gerald |last=Burns |title=Solid State Physics |date=1985 |publisher=Academic Press, Inc. |isbn=978-0-12-146070-9 |pages=339–40}}</ref> A few terms are widely used, but without any very formal definition, such as "[[heavy metals|heavy metal]]", which has been given such a wide range of definitions that it has been criticized as "effectively meaningless".<ref>{{cite journal |last1=Duffus |first1=John H. |date=2002 |title="Heavy Metals"–A Meaningless Term? |url=https://publications.iupac.org/pac/2002/pdf/7405x0793.pdf |journal=Pure and Applied Chemistry |volume=74 |issue=5 |pages=793–807 |doi=10.1351/pac200274050793 |s2cid=46602106 |access-date=27 March 2021 |archive-date=11 April 2021 |archive-url=https://web.archive.org/web/20210411012337/https://publications.iupac.org/pac/2002/pdf/7405x0793.pdf |url-status=live }}</ref> The scope of terms varies significantly between authors. For example, according to IUPAC, the noble gases extend to include the whole group, including the very radioactive superheavy element oganesson.<ref>{{cite journal|last=Koppenol|first=W.|date=2016|title=How to name new chemical elements|journal=Pure and Applied Chemistry|publisher=DeGruyter|doi=10.1515/pac-2015-0802 |hdl=10045/55935|s2cid=102245448|url=https://rua.ua.es/dspace/bitstream/10045/55935/1/2016_Koppenol_etal_PureApplChem.pdf|hdl-access=free|access-date=15 August 2021|archive-date=11 May 2020|archive-url=https://web.archive.org/web/20200511193435/https://rua.ua.es/dspace/bitstream/10045/55935/1/2016_Koppenol_etal_PureApplChem.pdf|url-status=live}}</ref> However, among those who specialize in the superheavy elements, this is not often done: in this case "noble gas" is typically taken to imply the unreactive behaviour of the lighter elements of the group. Since calculations generally predict that oganesson should not be particularly inert due to relativistic effects, and may not even be a gas at room temperature if it could be produced in bulk, its status as a noble gas is often questioned in this context.<ref>{{cite journal |last1=Roth |first1=Klaus |date=3 April 2018 |title=Is Element 118 a Noble Gas? |url=https://www.chemistryviews.org/details/ezine/10907570/New_Kids_on_the_Table_Is_Element_118_a_Noble_Gas__Part_1.html |journal=Chemie in unserer Zeit |doi=10.1002/chemv.201800029 |access-date=27 March 2021 |archive-date=2 March 2021 |archive-url=https://web.archive.org/web/20210302084128/https://www.chemistryviews.org/details/ezine/10907570/New_Kids_on_the_Table_Is_Element_118_a_Noble_Gas__Part_1.html |url-status=live |url-access=subscription }}</ref> Furthermore, national variations are sometimes encountered: in Japan, alkaline earth metals often do not include beryllium and magnesium as their behaviour is different from the heavier group 2 metals.<ref>{{cite web |url=https://www.chemistry.or.jp/news/information/1-2.html |title=【お知らせ】高等学校化学で用いる用語に関する提案(1)への反応 |author=The Chemical Society of Japan |date=25 January 2018 |website=www.chemistry.or.jp |publisher=The Chemical Society of Japan |access-date=3 April 2021 |quote=「12.アルカリ土類金属」の範囲についても,△を含めれば,すべての教科書で提案が考慮されている。歴史的には第4 周期のカルシウム以下を指していた用語だったが,「周期表の2 族に対応する用語とする」というIUPAC の勧告1)に従うのは現在では自然な流れだろう。 |archive-date=16 May 2021 |archive-url=https://web.archive.org/web/20210516062728/https://www.chemistry.or.jp/news/information/1-2.html |url-status=live }}</ref>
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