Editing Chemical element (section)

== Origin of the elements ==
{{main|Nucleosynthesis}}
[[File:Universe content pie chart.jpg|thumb|upright=1.2|Estimated distribution of dark matter and dark energy in the universe. Only the fraction of the mass and energy labeled "atoms" is composed of elements.]]
Only about 4% of the total mass of the universe is made of atoms or [[ion]]s, and thus represented by elements. This fraction is about 15% of the total matter, with the remainder of the matter (85%) being [[dark matter]]. The nature of dark matter is unknown, but it is not composed of atoms of elements because it contains no protons, neutrons, or electrons. (The remaining non-matter part of the mass of the universe is composed of the even less well understood [[dark energy]]).

The 94 naturally occurring elements were produced by at least four classes of astrophysical process. Most of the hydrogen, helium and a very small quantity of lithium were produced in the first few minutes of the [[Big Bang]]. This [[Big Bang nucleosynthesis]] happened only once; the other processes are ongoing. [[Nuclear fusion]] inside stars produces elements through stellar nucleosynthesis, including all elements from carbon to [[iron]] in atomic number. Elements higher in atomic number than iron, including heavy elements like uranium and plutonium, are produced by various forms of explosive nucleosynthesis in [[supernova]]e and [[neutron star merger]]s. The light elements [[lithium]], [[beryllium]] and [[boron]] are produced mostly through [[cosmic ray spallation]] (fragmentation induced by [[cosmic ray]]s) of carbon, nitrogen, and oxygen.

In the early phases of the Big Bang, nucleosynthesis of hydrogen resulted in the production of hydrogen-1 (protium, {{sup|1}}H) and helium-4 ({{sup|4}}He), as well as a smaller amount of deuterium ({{sup|2}}H) and tiny amounts (on the order of 10{{sup|−10}}) of lithium and beryllium. Even smaller amounts of boron may have been produced in the Big Bang, since it has been observed in some very old stars, while carbon has not.<ref>{{cite news|last=Wilford|first=J.N.|date=14 January 1992|title=Hubble Observations Bring Some Surprises|url=https://query.nytimes.com/gst/fullpage.html?res=9E0CE5D91F3AF937A25752C0A964958260|newspaper=[[The New York Times]]|access-date=15 February 2017|archive-date=5 March 2008|archive-url=https://web.archive.org/web/20080305211140/http://query.nytimes.com/gst/fullpage.html?res=9E0CE5D91F3AF937A25752C0A964958260|url-status=live}}</ref> No elements heavier than boron were produced in the Big Bang. As a result, the primordial abundance of atoms (or ions) consisted of ~75% {{sup|1}}H, 25% {{sup|4}}He, and 0.01% deuterium, with only tiny traces of lithium, beryllium, and perhaps boron.<ref>{{cite web|last=Wright|first=E. L.|date=12 September 2004|title=Big Bang Nucleosynthesis|url=http://www.astro.ucla.edu/~wright/BBNS.html|publisher=[[UCLA]], Division of Astronomy|access-date=22 February 2007|archive-date=13 January 2018|archive-url=https://web.archive.org/web/20180113051655/http://astro.ucla.edu/~wright/BBNS.html|url-status=live}}</ref> Subsequent enrichment of [[galactic spheroid|galactic halos]] occurred due to stellar nucleosynthesis and [[supernova nucleosynthesis]].<ref name="synthesis">{{cite journal|year=1999 |title=Synthesis of the elements in stars: forty years of progress |url=http://www.cococubed.com/papers/wallerstein97.pdf |journal=[[Reviews of Modern Physics]] |volume=69 |issue=4 |pages=995–1084 |doi=10.1103/RevModPhys.69.995 |bibcode=1997RvMP...69..995W |last1=Wallerstein |first1=George |last2=Iben |first2=Icko |last3=Parker |first3=Peter |last4=Boesgaard |first4=Ann |last5=Hale |first5=Gerald |last6=Champagne |first6=Arthur |last7=Barnes |first7=Charles |last8=Käppeler |first8=Franz |last9=Smith |first9=Verne |display-authors=8 |url-status=dead |archive-url=https://web.archive.org/web/20060928043229/http://www.cococubed.com/papers/wallerstein97.pdf |archive-date=28 September 2006 |hdl=2152/61093 |hdl-access=free }}</ref> However, the element abundance in [[intergalactic space]] can still closely resemble primordial conditions, unless it has been enriched by some means.

[[File:Nucleosynthesis periodic table.svg|thumb|upright=1.78|Periodic table showing the cosmogenic origin of each element in the Big Bang, or in large or small stars. Small stars can produce certain elements up to sulfur, by the [[alpha process]]. Supernovae are needed to produce "heavy" elements (those beyond iron and nickel) rapidly by neutron buildup, in the [[r-process]]. Certain large stars slowly produce other elements heavier than iron, in the [[s-process]]; these may then be blown into space in the off-gassing of [[planetary nebulae]]]]

On Earth (and elsewhere), trace amounts of various elements continue to be produced from other elements as products of [[nuclear transmutation]] processes. These include some produced by [[cosmic ray]]s or other nuclear reactions (see [[cosmogenic]] and [[nucleogenic]] nuclides), and others produced as [[decay product]]s of long-lived primordial nuclides.<ref name="Earnshaw1997">{{cite book|last1=Earnshaw|first1=A.|last2=Greenwood|first2=N.|year=1997|title=Chemistry of the Elements|edition=2nd|publisher=[[Butterworth-Heinemann]]}}</ref> For example, trace (but detectable) amounts of [[carbon-14]] ({{sup|14}}C) are continually produced in the air by cosmic rays impacting nitrogen atoms, and argon-40 ({{sup|40}}Ar) is continually produced by the decay of primordially occurring but unstable potassium-40 ({{sup|40}}K). Also, three primordially occurring but radioactive actinides, thorium, uranium, and plutonium, decay through a series of recurrently produced but unstable elements such as radium and [[radon]], which are transiently present in any sample of containing these metals. Three other radioactive elements, technetium, promethium, and neptunium, occur only incidentally in natural materials, produced as individual atoms by [[nuclear fission]] of the nuclei of various heavy elements or in other rare nuclear processes.

Besides the 94 naturally occurring elements, several [[artificial element]]s have been produced by [[nuclear physics]] technology. By 2016, these experiments had produced all elements up to atomic number 118.