Editing Chemical element (section)

== History<!--linked from 'Classical element'--> ==
=== Evolving definitions ===
The concept of an "element" as an indivisible substance has developed through three major historical phases: Classical definitions (such as those of the ancient Greeks), chemical definitions, and atomic definitions.

=== Classical definitions ===
{{Main|Classical element#Hellenistic philosophy}}
[[Ancient philosophy]] posited a set of [[classical element]]s to explain observed patterns in [[nature]]. These ''elements'' originally referred to ''[[Earth (classical element)|earth]]'', ''[[Water (classical element)|water]]'', ''[[Air (classical element)|air]]'' and ''[[Fire (classical element)|fire]]'' rather than the chemical elements of modern science.

The term 'elements' (''stoicheia'') was first used by Greek philosopher [[Plato]] around 360&nbsp;BCE in his dialogue [[Timaeus (dialogue)|Timaeus]], which includes a discussion of the composition of inorganic and organic bodies and is a speculative treatise on chemistry. Plato believed the elements introduced a century earlier by [[Empedocles]] were composed of small [[regular polyhedron|polyhedral]] [[Theory of Forms|forms]]: [[tetrahedron]] (fire), [[octahedron]] (air), [[icosahedron]] (water), and [[cube]] (earth).<ref>{{cite book|author=Plato|year=2008|orig-year=c. 360 BC|title=Timaeus|url=https://books.google.com/books?id=xSjvowNydN8C&q=Plato%20timaeus&pg=PA45|publisher=Forgotten Books|page=45|isbn=978-1-60620-018-6|access-date=9 November 2020|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414140053/https://books.google.com/books?id=xSjvowNydN8C&q=Plato%20timaeus&pg=PA45|url-status=live}}</ref><ref>{{cite web|last=Hillar |first=M. |year=2004 |title=The Problem of the Soul in Aristotle's De anima |url=http://www.socinian.org/aristotles_de_anima.html |publisher=[[NASA]]/[[WMAP]] |access-date=10 August 2006 |url-status=dead |archive-url=https://web.archive.org/web/20060909004214/http://www.socinian.org/aristotles_de_anima.html |archive-date=9 September 2006 }}</ref>

[[Aristotle]], {{circa|350 BCE}}, also used the term ''stoicheia'' and added a fifth element, [[Aether (classical element)|aether]], which formed the heavens. Aristotle defined an element as:

{{blockquote|Element – one of those bodies into which other bodies can decompose, and that itself is not capable of being divided into other.<ref>{{cite book|last=Partington|first=J. R.|year=1937|title=A Short History of Chemistry|location=New York|publisher=Dover Publications|isbn=978-0-486-65977-0|url-access=registration|url=https://archive.org/details/shorthistoryofch0000part_q6h4}}</ref>}}

=== Chemical definitions ===

==== Robert Boyle ====
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[[File:Portret van Robert Boyle, RP-P-OB-4578 (cropped).jpg|thumb|200x200px|Robert Boyle, {{circa|1740}}]]
[[File:Sceptical chymist 1661 Boyle Title page AQ18 (3).jpg|thumb|330x330px|Title page of ''The Sceptical Chymist,'' published in 1661]]

In 1661, in ''[[The Sceptical Chymist]]'', [[Robert Boyle]] proposed his theory of corpuscularism which favoured the analysis of matter as constituted of irreducible units of matter (atoms); and, choosing to side with neither Aristotle's view of the four elements nor [[Paracelsus]]' view of three fundamental elements, left open the question of the number of elements. Boyle argued against a pre-determined number of elements—directly against Paracelsus' three [[Principle (chemistry)|principles]] (sulfur, mercury, and salt), indirectly against the [[Classical element|"Aristotelian" elements]] (earth, water, air, and fire), for Boyle felt that the arguments against the former were at least as valid against the latter.
{{Blockquote|text=Much of what I am to deliver ... may be indifferently apply'd to the four Peripatetick Elements, and the three Chymical Principles ... the Chymical ''Hypothesis'' seeming to be much more countenanc'd by Experience then the other, it will be expedient to insist chiefly upon the disproving of that; especially since most of the Arguments that are imploy'd against it, may, by a little variation, be made ... at least as strongly against the less plausible, ''Aristotelian'' Doctrine.{{Sfn|Boyle|1661|p=36}}}}

Then Boyle stated his view in four propositions. In the first and second, he suggests that matter consists of particles, but that these particles may be difficult to separate. Boyle used the concept of "corpuscles"—or "atomes",{{Sfn|Boyle|1661|p=38}} as he also called them—to explain how a limited number of elements could combine into a vast number of compounds.

{{Blockquote|text='''Propos. I.''' ''... At the first Production of mixt Bodies, the Universal Matter whereof they ... consisted, was actually divided into little Particles.''{{Sfn|Boyle|1661|p=37}} ... The Generation ... and wasting of Bodies ... and ... the Chymical Resolutions of mixt Bodies, and ... Operations of ... Fires upon them ... manifest their consisting of parts very minute...  ''Epicurus'' ... as you well know, supposes ... all ... Bodies ... to be produc'd by ... Atomes, moving themselves to and fro ... in the ... Infinite ''Vacuum''.{{Sfn|Boyle|1661|pp=37–38}} ... '''Propos. II.''' ''... These minute Particles ... were ... associated into minute ... Clusters ... not easily dissipable into such Particles as compos'd them.''{{Sfn|Boyle|1661|pp=38–39}} ... If we assigne to the Corpuscles, whereof each Element consists, a peculiar size and shape ... such ... Corpuscles may be mingled in such various Proportions, and ... connected so many ... wayes, that an almost incredible number of ... Concretes may be compos'd of them.{{Sfn|Boyle|1661|p=42}}}}

Boyle explained that gold reacts with ''[[aqua regia]],'' and mercury with nitric acid, sulfuric acid, and sulfur to produce various "compounds", and that they could be recovered from those compounds, just as would be expected of elements. Yet, Boyle did not consider gold,{{Sfn|Boyle|1661|p=29}} mercury,{{Sfn|Boyle|1661|p=41}} or lead{{Sfn|Boyle|1661|p=29}} elements, but rather—together with wine{{Sfn|Boyle|1661|p=145}}—"perfectly mixt bodies". 
{{Blockquote|text=Quicksilver ... with ''Aqua fortis'' will be brought into a ... white Powder ... with Sulphur it will compose a blood-red ... Cinaber. And yet out of all these exotick Compounds, we may recover the very same running Mercury.{{Sfn|Boyle|1661|pp=40–41}} ... '''Propos. III.''' ''... From most of such mixt Bodies ... there may by the Help of the Fire, be actually obtain'd a determinate number (whether Three, Four or Five, or fewer or more) of Substances ...''
The Chymists are wont to call the Ingredients of mixt Bodies, ''Principles'', as the ''Aristotelians'' name them ''Elements''. ... ''Principles'' ... as not being compounded of any more primary Bodies: and ''Elements'', in regard that all mix'd Bodies are compounded of them.{{Sfn|Boyle|1661|p=46}}}}

Even though Boyle is primarily regarded as the first modern chemist, ''The Sceptical Chymist'' still contains old ideas about the elements, alien to a contemporary viewpoint. Sulfur, for example, is not only the familiar yellow non-metal but also an inflammable "spirit".{{Sfn|Boyle|1661|p=145}}

==== Isaac Watts ====
[[File:Portrait of Isaac Watts, D.D..jpg|thumb|216x216px|Portrait of Isaac Watts by John Shury, {{circa|1830}}]]
In 1724, in his book ''[[Logick]]'', the English minister and logician [[Isaac Watts]] enumerated the elements then recognised by chemists. Watts' list of elements included two of Paracelsus' ''principles'' (sulfur and salt) and two classical elements (earth and water) as well as "spirit". Watts did, however, note a lack of consensus among chemists.<ref>{{Cite book |last=Watts |first=Isaac |url=https://archive.org/details/logickorrightuse00wattuoft/page/13/mode/1up |title=Logick: Or, the right use of reason in the enquiry after truth, with a variety of rules to guard against error in the affairs of religion and human life, as well as in the sciences |publisher=Printed for John Clark and Richard Hett |year=1726 |pages=13–15 |orig-date=1724}}</ref>
{{Blockquote|text=Elements are such Substances as cannot be resolved, or reduced, into two or more Substances of different Kinds. ... Followers of Aristotle made Fire, Air, Earth and Water to be the four Elements, of which all earthly Things were compounded; and they suppos'd the Heavens to be a Quintessence, or fifth sort of Body, distinct from all these : But, since experimental Philosophy ... have been better understood, this Doctrine has been abundantly refuted. The Chymists make Spirit, Salt, Sulphur, Water and Earth to be their five Elements, because they can reduce all terrestrial Things to these five :.. tho' they are not all agreed.}}

==== Antoine Lavoisier, Jöns Jacob Berzelius, and Dmitri Mendeleev ====
[[File:Mendeleev's 1869 periodic table.svg|upright=1.35|thumb|[[Mendeleev]]'s 1869 periodic table: ''An experiment on a system of elements. Based on their atomic weights and chemical similarities.'']]The first modern list of elements was given in [[Antoine Lavoisier]]'s 1789 ''[[Traité Élémentaire de Chimie|Elements of Chemistry]]'', which contained 33 elements, including [[light]] and [[Caloric theory|caloric]].<ref>{{cite book|last=Lavoisier|first=A. L.|year=1790|title=Elements of chemistry translated by Robert Kerr|url=https://books.google.com/books?id=4BzAjCpEK4gC&pg=PA175|place=Edinburgh|pages=175–176|isbn=978-0-415-17914-0|access-date=24 August 2020|archive-date=14 April 2021|archive-url=https://web.archive.org/web/20210414100525/https://books.google.com/books?id=4BzAjCpEK4gC&pg=PA175|url-status=live}}</ref><ref>{{Cite book |last=Lavoisier |first=Antoine |author-link=Antoine Lavoisier |url=https://www.gutenberg.org/cache/epub/30775/pg30775-images.html#Page_175 |title=Elements of chemistry: In a new systematic order, containing all the modern discoveries: Illustrated with thirteen copperplates |publisher=William Creech |year=1790 |pages=175–176 |language=en |translator-last=Kerr |translator-first=Robert |orig-date=1789}}</ref> By 1818, [[Jöns Jacob Berzelius]] had determined atomic weights for 45 of the 49 then-accepted elements. [[Dmitri Mendeleev]] had 63 elements in his 1869 periodic table.
[[File:DIMendeleevCab.jpg|thumb|left|upright|Dmitri Mendeleev, 1897]]
From Boyle until the early 20th century, an element was defined as a pure substance that cannot be decomposed into any simpler substance and cannot be transformed into other elements by chemical processes. Elements at the time were generally distinguished by their atomic weights, a property measurable with fair accuracy by available analytical techniques.

=== Atomic definitions ===
[[File:Henry Moseley.jpg|thumb|upright=1.0|[[Henry Moseley]]]]

The 1913 discovery by English physicist [[Henry Moseley]] that the nuclear charge is the physical basis for the atomic number, further refined when the nature of protons and [[neutron]]s became appreciated, eventually led to the current definition of an element based on atomic number (number of protons). The use of atomic numbers, rather than atomic weights, to distinguish elements has greater predictive value (since these numbers are integers) and also resolves some ambiguities in the chemistry-based view due to varying properties of isotopes and [[allotrope]]s within the same element. Currently, IUPAC defines an element to exist if it has isotopes with a lifetime longer than the 10{{sup|−14}} seconds it takes the nucleus to form an electronic cloud.<ref>[http://www.kernchemie.de/Transactinides/Transactinide-2/transactinide-2.html Transactinide-2] {{Webarchive|url=https://web.archive.org/web/20160303222840/http://www.kernchemie.de/Transactinides/Transactinide-2/transactinide-2.html |date=3 March 2016 }}. www.kernchemie.de</ref>

By 1914, eighty-seven elements were known, all naturally occurring (see [[Discovery of chemical elements]]). The remaining naturally occurring elements were discovered or isolated in subsequent decades, and various additional elements have also been produced synthetically, with much of that work pioneered by [[Glenn T. Seaborg]]. In 1955, element 101 was discovered and named [[mendelevium]] in honor of D. I. Mendeleev, the first to arrange the elements periodically.

=== Discovery and recognition of various elements ===
{{For timeline|Discovery of chemical elements}}

Ten materials familiar to various prehistoric cultures are now known to be elements: Carbon, copper, [[gold]], iron, lead, mercury, silver, sulfur, [[tin]], and [[zinc]]. Three additional materials now accepted as elements, [[arsenic]], [[antimony]], and [[bismuth]], were recognised as distinct substances before 1500 AD. [[Phosphorus]], [[cobalt]], and [[platinum]] were isolated before 1750.

Most of the remaining naturally occurring elements were identified and characterised by 1900, including:
* Such now-familiar [[Industry (manufacturing)|industrial]] materials as [[aluminium]], [[silicon]], [[nickel]], [[chromium]], magnesium, and tungsten
* Reactive metals such as [[lithium]], [[sodium]], potassium, and [[calcium]]
* The [[halogen]]s [[fluorine]], [[chlorine]], [[bromine]], and [[iodine]]
* Gases such as hydrogen, oxygen, nitrogen, helium, [[argon]], and [[neon]]
* Most of the [[rare-earth elements]], including [[cerium]], [[lanthanum]], [[gadolinium]], and [[neodymium]]
* The more common [[radioactive]] elements, including uranium, thorium, and [[radium]]

Elements isolated or produced since 1900 include:
* The three remaining undiscovered stable elements: [[hafnium]], [[lutetium]], and [[rhenium]]
* [[Plutonium]], which was first produced synthetically in 1940 by [[Glenn T. Seaborg]], but is now also known from a few long-persisting natural occurrences
* The three incidentally occurring natural elements ([[neptunium]], promethium, and technetium), which were all first produced synthetically but later discovered in trace amounts in geological samples
* Four scarce decay products of uranium or thorium (astatine, francium, [[actinium]], and [[protactinium]]), and
* All synthetic [[transuranic]] elements, beginning with [[americium]] and [[curium]]

=== Recently discovered elements ===
The first [[transuranium element]] (element with an atomic number greater than 92) discovered was [[neptunium]] in 1940. Since 1999, the [[IUPAC/IUPAP Joint Working Party]] has considered claims for the discovery of new elements. As of January 2016, all 118 elements have been confirmed by IUPAC as being discovered. The discovery of element 112 was acknowledged in 2009, and the name ''copernicium'' and the chemical symbol ''Cn'' were suggested for it.<ref>{{cite web|date=20 July 2009|title=IUPAC Announces Start of the Name Approval Process for the Element of Atomic Number 112|url=http://media.iupac.org/news/112_Naming_Process_20090720.pdf|publisher=IUPAC|access-date=27 August 2009|archive-date=13 March 2012|archive-url=https://web.archive.org/web/20120313014559/http://media.iupac.org/news/112_Naming_Process_20090720.pdf|url-status=live}}</ref> The name and symbol were officially endorsed by IUPAC on 19 February 2010.<ref>{{cite web|date=20 February 2010 |title= Element 112 is Named Copernicium |url=http://www.iupac.org/web/nt/2010-02-20_112_Copernicium |publisher=IUPAC |url-status=dead |archive-url=https://web.archive.org/web/20100224054826/http://www.iupac.org/web/nt/2010-02-20_112_Copernicium |archive-date=24 February 2010 }}</ref> The heaviest element that is believed to have been synthesised to date is element 118, [[oganesson]], on 9 October 2006, by the [[Joint Institute for Nuclear Research|Flerov Laboratory]] of Nuclear Reactions in [[Dubna]], Russia.{{r|Schewe}}<ref>{{cite journal|year=2006|title=Evidence for Dark Matter |journal=[[Physical Review C]]|volume=74|issue=4|pages=044602|doi=10.1103/PhysRevC.74.044602|bibcode=2006PhRvC..74d4602O |bibcode-access=free |last1=Oganessian|first1=Yu. Ts.|last2=Utyonkov|first2=V.|last3=Lobanov|first3=Yu.|last4=Abdullin|first4=F.|last5=Polyakov|first5=A.|last6=Sagaidak|first6=R.|last7=Shirokovsky|first7=I.|last8=Tsyganov|first8=Yu.|last9=Voinov|first9=A.|display-authors=8|doi-access=free}}</ref> [[Tennessine]], element 117 was the latest element claimed to be discovered, in 2009.<ref name="jinr">{{cite web|last=Greiner |first=W. |title=Recommendations |url=http://www.jinr.ru/img_sections/PAC/NP/31/PAK_NP_31_recom_eng.pdf |work=31st meeting, PAC for Nuclear Physics |publisher=[[Joint Institute for Nuclear Research]] |url-status=dead |archive-url=https://web.archive.org/web/20100414173735/http://www.jinr.ru/img_sections/PAC/NP/31/PAK_NP_31_recom_eng.pdf |archive-date=14 April 2010 }}</ref> On 28 November 2016, scientists at the IUPAC officially recognised the names for the four newest elements, with atomic numbers 113, 115, 117, and 118.<ref name="IUPAC-20161130">{{cite news |author=Staff |title=IUPAC Announces the Names of the Elements 113, 115, 117, and 118 |url=https://iupac.org/iupac-announces-the-names-of-the-elements-113-115-117-and-118/ |date=30 November 2016 |work=IUPAC |access-date=1 December 2016 |archive-date=29 July 2018 |archive-url=https://web.archive.org/web/20180729210456/https://iupac.org/iupac-announces-the-names-of-the-elements-113-115-117-and-118/ |url-status=live }}</ref><ref name="NYT-20161201">{{cite news |last=St. Fleur |first=Nicholas |title=Four New Names Officially Added to the Periodic Table of Elements |url=https://www.nytimes.com/2016/12/01/science/periodic-table-new-elements.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2016/12/01/science/periodic-table-new-elements.html |archive-date=2022-01-01 |url-access=limited |date=1 December 2016 |work=[[The New York Times]] |access-date=1 December 2016 }}{{cbignore}}</ref>