Editing Hydrogen (section)

==== Isotopes ====
{{Main|Isotopes of hydrogen}}
[[File:Blausen 0530 HydrogenIsotopes.png|thumb|left|The three naturally-occurring isotopes of hydrogen: hydrogen-1 (protium), hydrogen-2 (deuterium), and hydrogen-3 (tritium)|alt=Diagram showing the structure of each of Hydrogen-1 (mass number 1, 1 electron, 1 proton), Hydrogen-2 or deuterium (mass number 2, 1 electron, 1 proton, 1 neutron), and Hydrogen-3 or tritium (mass number 3, 1 electron, 1 proton, 2 neutrons)]]
Hydrogen has three naturally occurring isotopes, denoted {{chem|1|H}}, {{chem|2|H}} and {{chem|3|H}}. Other, highly unstable nuclei ({{chem|4|H}} to {{chem|7|H}}) have been synthesized in the laboratory but not observed in nature.<ref name="Gurov">{{cite journal
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'''{{chem|1|H}}''' is the most common hydrogen isotope, with an abundance of >99.98%. Because the [[atomic nucleus|nucleus]] of this isotope consists of only a single proton, it is given the descriptive but rarely used formal name ''protium''.<ref>{{cite journal
|last1=Urey|first1=H. C.
|last2=Brickwedde|first2=F. G.|last3=Murphy|first3=G. M.
|title=Names for the Hydrogen Isotopes
|journal=Science|date=1933|volume=78
|issue=2035|pages=602–603
|doi=10.1126/science.78.2035.602
|pmid=17797765|bibcode = 1933Sci....78..602U }}</ref> It is the only stable isotope with no neutrons; see [[Isotopes of helium#Helium-2 (diproton)|diproton]] for a discussion of why others do not exist.<ref>{{NUBASE2020}}</ref>

'''{{chem|2|H}}''', the other stable hydrogen isotope, is known as [[deuterium]] and contains one proton and one [[neutron]] in the nucleus. Nearly all deuterium nuclei in the universe is thought to have been produced at the time of the [[Big Bang]], and has endured since then.<ref>{{Cite journal |last1=Particle Data Group |last2=Workman |first2=R L |last3=Burkert |first3=V D |last4=Crede |first4=V |last5=Klempt |first5=E |last6=Thoma |first6=U |last7=Tiator |first7=L |last8=Agashe |first8=K |last9=Aielli |first9=G |last10=Allanach |first10=B C |last11=Amsler |first11=C |last12=Antonelli |first12=M |last13=Aschenauer |first13=E C |last14=Asner |first14=D M |last15=Baer |first15=H |date=2022-08-08 |title=Review of Particle Physics |url=https://academic.oup.com/ptep/article/doi/10.1093/ptep/ptac097/6651666 |journal=Progress of Theoretical and Experimental Physics |language=en |volume=2022 |issue=8 |doi=10.1093/ptep/ptac097 |issn=2050-3911|hdl=1854/LU-01HQG4F6CV7P2F3WWNH4RRN8HD |hdl-access=free }}</ref>{{rp|loc=24.2}} Deuterium is not radioactive, and is not a significant toxicity hazard. Water enriched in molecules that include deuterium instead of normal hydrogen is called [[heavy water]]. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for {{chem|1|H}}-[[NMR spectroscopy]].<ref>{{cite journal
|author=Oda, Y.
|author2=Nakamura, H.
|author3=Yamazaki, T.
|author4=Nagayama, K.
|author5=Yoshida, M.
|author6=Kanaya, S.
|author7=Ikehara, M.
|title=1H NMR studies of deuterated ribonuclease HI selectively labeled with protonated amino acids
|journal=[[Journal of Biomolecular NMR]]
|date=1992|volume=2|issue=2|pages=137–47
|doi=10.1007/BF01875525
|pmid=1330130|s2cid=28027551
}}</ref> Heavy water is used as a [[neutron moderator]] and coolant for nuclear reactors. Deuterium is also a potential fuel for commercial [[nuclear fusion]].<ref>{{cite news
|last=Broad
|first=W. J.
|date=11 November 1991
|title=Breakthrough in Nuclear Fusion Offers Hope for Power of Future
|work=The New York Times
|url=https://query.nytimes.com/gst/fullpage.html?res=9D0CE4D81030F932A25752C1A967958260
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|archive-date=29 January 2021
|archive-url=https://web.archive.org/web/20210129015717/https://www.nytimes.com/1991/11/11/us/breakthrough-in-nuclear-fusion-offers-hope-for-power-of-future.html
|url-status=live
}}</ref> 

'''{{chem|3|H}}''' is known as [[tritium]] and contains one proton and two neutrons in its nucleus. It is radioactive, decaying into [[helium-3]] through [[beta decay]] with a [[half-life]] of 12.32 years.<ref name="Miessler" /> It is radioactive enough to be used in [[Radioluminescent paint|luminous paint]] to enhance the visibility of data displays, such as for painting the hands and dial-markers of watches. The watch glass prevents the small amount of radiation from escaping the case.<ref name="Traub95">{{cite web|last1=Traub|first1=R. J.|last2=Jensen|first2=J. A.|title=Tritium radioluminescent devices, Health and Safety Manual|url=http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/27/001/27001618.pdf|publisher=International Atomic Energy Agency|access-date=20 May 2015|page=2.4|date=June 1995|archive-url=https://web.archive.org/web/20150906043743/http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/27/001/27001618.pdf|archive-date=6 September 2015|url-status=live}}</ref> Small amounts of tritium are produced naturally by cosmic rays striking atmospheric gases; tritium has also been released in [[nuclear testing|nuclear weapons tests]].<ref>{{cite web| author=Staff| date=15 November 2007| url=http://www.epa.gov/rpdweb00/radionuclides/tritium.html| publisher=U.S. Environmental Protection Agency| title=Tritium| access-date=12 February 2008| archive-url=https://web.archive.org/web/20080102171148/http://www.epa.gov/rpdweb00/radionuclides/tritium.html| archive-date=2 January 2008| url-status=live}}</ref> It is used in nuclear fusion,<ref>{{cite web| last=Nave| first=C. R.| title=Deuterium-Tritium Fusion| work=HyperPhysics| publisher=Georgia State University| date=2006| url=http://hyperphysics.phy-astr.gsu.edu/Hbase/nucene/fusion.html| access-date=8 March 2008| archive-url=https://web.archive.org/web/20080316055852/http://hyperphysics.phy-astr.gsu.edu/Hbase/nucene/fusion.html| archive-date=16 March 2008| url-status=live}}</ref> as a tracer in [[isotope geochemistry]],<ref>{{cite journal| first1=C.| last1=Kendall| first2=E.| last2=Caldwell| journal=Isotope Tracers in Catchment Hydrology| title=Chapter 2: Fundamentals of Isotope Geochemistry| editor1=C. Kendall| editor2=J. J. McDonnell| publisher=US Geological Survey| date=1998| doi=10.1016/B978-0-444-81546-0.50009-4| url=http://wwwrcamnl.wr.usgs.gov/isoig/isopubs/itchch2.html#2.5.1| access-date=8 March 2008| archive-url=https://web.archive.org/web/20080314192517/http://wwwrcamnl.wr.usgs.gov/isoig/isopubs/itchch2.html#2.5.1| archive-date=14 March 2008| pages=51–86}}</ref> and in specialized [[self-powered lighting]] devices.<ref>{{cite web| title=The Tritium Laboratory| publisher=University of Miami| date=2008| url=http://www.rsmas.miami.edu/groups/tritium/| access-date=8 March 2008| archive-url=https://web.archive.org/web/20080228061358/http://www.rsmas.miami.edu/groups/tritium/| archive-date=28 February 2008| df=dmy-all}}</ref> Tritium has also been used in chemical and biological labeling experiments as a [[radiolabel]].<ref name="holte">{{cite journal| last1=Holte| first1=A. E.| last2=Houck| first2=M. A.| last3=Collie| first3=N. L.| title=Potential Role of Parasitism in the Evolution of Mutualism in Astigmatid Mites| journal=Experimental and Applied Acarology| volume=25| issue=2| pages=97–107| date=2004|doi=10.1023/A:1010655610575| pmid=11513367| s2cid=13159020}}</ref>

Unique among the elements, distinct names are assigned to its isotopes in common use. During the early study of radioactivity, heavy radioisotopes were given their own names, but these are mostly no longer used. The symbols D and T (instead of {{chem|2|H}} and {{chem|3|H}}) are sometimes used for deuterium and tritium, but the symbol P was already used for [[phosphorus]] and thus was not available for protium.<ref>{{cite web|last=van der Krogt|first=P.|date=5 May 2005|url=http://elements.vanderkrogt.net/element.php?sym=H|publisher=Elementymology & Elements Multidict|title=Hydrogen|access-date=20 December 2010|archive-url=https://web.archive.org/web/20100123001440/http://elements.vanderkrogt.net/element.php?sym=H|archive-date=23 January 2010}}</ref> In its [[IUPAC nomenclature|nomenclatural]] guidelines, the [[International Union of Pure and Applied Chemistry]] (IUPAC) allows any of D, T, {{chem|2|H}}, and {{chem|3|H}} to be used, though {{chem|2|H}} and {{chem|3|H}} are preferred.<ref>§ IR-3.3.2, [http://old.iupac.org/reports/provisional/abstract04/RB-prs310804/Chap3-3.04.pdf Provisional Recommendations] {{Webarchive|url=https://web.archive.org/web/20160209043933/http://old.iupac.org/reports/provisional/abstract04/RB-prs310804/Chap3-3.04.pdf |date=9 February 2016 }}, Nomenclature of Inorganic Chemistry, Chemical Nomenclature and Structure Representation Division, IUPAC. Accessed on line 3 October 2007.</ref>

[[Antihydrogen]] ({{physics particle|anti=yes|H}}) is the [[antimatter]] counterpart to hydrogen. It consists of an [[antiproton]] with a [[positron]]. Antihydrogen is the only type of antimatter atom to have been produced {{as of|2015|lc=y}}.<ref name="char15">{{cite journal|last1=Charlton|first1=Mike|last2=Van Der Werf|first2=Dirk Peter|title=Advances in antihydrogen physics|journal=Science Progress|date=1 March 2015|volume=98|issue=1|pages=34–62|doi=10.3184/003685015X14234978376369|pmid=25942774|pmc=10365473 |s2cid=23581065}}</ref><ref name="Keller15">{{cite journal|last1=Kellerbauer|first1=Alban|title=Why Antimatter Matters|journal=European Review|date=29 January 2015|volume=23|issue=1|pages=45–56|doi=10.1017/S1062798714000532|s2cid=58906869}}</ref> The [[exotic atom]] [[muonium]] (symbol Mu), composed of an anti[[muon]] and an [[electron]], is analogous hydrogen and IUPAC nomenclature incorporates such hypothetical compounds as muonium chloride (MuCl) and sodium muonide (NaMu), analogous to [[hydrogen chloride]] and [[sodium hydride]] respectively.<ref name="iupac">{{cite journal
 |doi=10.1351/pac200173020377
 |author=W. H. Koppenol
 |author2=IUPAC
 |author2-link=International Union of Pure and Applied Chemistry
 |year=2001
 |title=Names for muonium and hydrogen atoms and their ions
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|url-status=live
 }}</ref>