Editing Hydrogen (section)

== History ==
{{Main|Timeline of hydrogen technologies}}

=== 18th century ===
[[File:Portret van Robert Boyle, RP-P-OB-4578 (cropped).jpg|thumb|[[Robert Boyle]], who discovered the reaction between [[iron filings]] and dilute acids]]
In 1671, Irish scientist [[Robert Boyle]] discovered and described the reaction between [[iron]] filings and dilute [[acid]]s, which results in the production of hydrogen gas.<ref>{{Cite book |last=Boyle |first=R. |url=https://quod.lib.umich.edu/e/eebo2/A29057.0001.001?rgn=main;view=fulltext |title=Tracts written by the Honourable Robert Boyle containing new experiments, touching the relation betwixt flame and air, and about explosions, an hydrostatical discourse occasion'd by some objections of Dr. Henry More against some explications of new experiments made by the author of these tracts: To which is annex't, an hydrostatical letter, dilucidating an experiment about a way of weighing water in water, new experiments, of the positive or relative levity of bodies under water, of the air's spring on bodies under water, about the differing pressure of heavy solids and fluids |publisher=Printed for Richard Davis |year=1672 |pages=64–65}}</ref><ref>{{cite web
|first=M.
|last=Winter
|date=2007
|url=http://education.jlab.org/itselemental/ele001.html
|title=Hydrogen: historical information
|publisher=WebElements Ltd
|access-date=5 February 2008
|archive-url=https://web.archive.org/web/20080410102154/http://education.jlab.org/itselemental/ele001.html
|archive-date=10 April 2008
}}</ref>
Boyle did not note that the gas was inflammable, but hydrogen would play a key role in overturning the [[phlogiston theory]] of combustion.<ref name=Ramsay-1896>{{Cite book |last=Ramsay |first=W. |url=https://www.gutenberg.org/files/52778/52778-h/52778-h.htm |title=The gases of the atmosphere: The history of their discovery |publisher=Macmillan |year=1896 |pages=19}}</ref>

In 1766, [[Henry Cavendish]] was the first to recognize hydrogen gas as a discrete substance, by naming the gas from a [[metal-acid reaction]] "inflammable air". He speculated that "inflammable air" was in fact identical to the hypothetical substance "[[Phlogiston theory|phlogiston]]"<ref>{{cite book |last = Musgrave
 |first = A.
 |chapter = Why did oxygen supplant phlogiston? Research programmes in the Chemical Revolution
 |title = Method and appraisal in the physical sciences
 |series = The Critical Background to Modern Science, 1800–1905
 |editor = Howson, C.
 |year = 1976
 |publisher = Cambridge University Press
 |access-date = 22 October 2011
 |chapter-url = http://ebooks.cambridge.org/chapter.jsf?bid=CBO9780511760013&cid=CBO9780511760013A009
 |doi = 10.1017/CBO9780511760013
 |isbn = 978-0-521-21110-9
 |url-access = registration
 |url = https://archive.org/details/methodappraisali0000unse
}}</ref><ref name="cav766">{{cite journal|last1=Cavendish|first1=Henry|title=Three Papers, Containing Experiments on Factitious Air, by the Hon. Henry Cavendish, F. R. S.|journal=Philosophical Transactions|date=12 May 1766|volume=56|pages=141–184|jstor=105491|bibcode=1766RSPT...56..141C|doi=10.1098/rstl.1766.0019|doi-access=free}}</ref> and further finding in 1781 that the gas produces water when burned. He is usually given credit for the discovery of hydrogen as an element.<ref name="Nostrand">{{cite encyclopedia| title=Hydrogen| encyclopedia=Van Nostrand's Encyclopedia of Chemistry| pages=797–799| publisher=Wylie-Interscience| year=2005| isbn=978-0-471-61525-5}}</ref><ref name="nbb">{{cite book| last=Emsley| first=John| title=Nature's Building Blocks| publisher=Oxford University Press| year=2001| location=Oxford| pages=183–191| isbn=978-0-19-850341-5}}</ref>

[[File:Antoine-Laurent Lavoisier by Louis Jean Desire Delaistre (cropped).jpg|thumb|[[Antoine Lavoisier]], who identified the element that came to be known as hydrogen]]
In 1783, [[Antoine Lavoisier]] identified the element that came to be known as hydrogen<ref>{{cite book| last=Stwertka| first=Albert| title=A Guide to the Elements| url=https://archive.org/details/guidetoelements00stwe| url-access=registration| publisher=Oxford University Press| year=1996| pages=[https://archive.org/details/guidetoelements00stwe/page/16 16–21]| isbn=978-0-19-508083-4}}</ref> when he and [[Pierre-Simon Laplace|Laplace]] reproduced Cavendish's finding that water is produced when hydrogen is burned.<ref name="nbb" /> Lavoisier produced hydrogen for his experiments on mass conservation by treating metallic [[iron]] with a stream of H<sub>2</sub>O through an incandescent iron tube heated in a fire. Anaerobic oxidation of iron by the protons of water at high temperature can be schematically represented by the set of following reactions:
*{{chem2|Fe + H2O -> FeO + H2}}
*{{chem2|2Fe + 3 H2O -> Fe2O3 + 3 H2}}
*{{chem2|3Fe + 4 H2O -> Fe3O4 + 4 H2}}

Many metals react similarly with water leading to the production of hydrogen.<ref>{{Cite journal |last1=Northwood |first1=D. O. |last2=Kosasih |first2=U. |date=1983 |title=Hydrides and delayed hydrogen cracking in zirconium and its alloys |url=https://journals.sagepub.com/doi/full/10.1179/imtr.1983.28.1.92 |journal=International Metals Reviews |language=en |volume=28 |issue=1 |pages=92–121 |doi=10.1179/imtr.1983.28.1.92 |issn=0308-4590}}</ref>  In some situations, this H<sub>2</sub>-producing process is problematic as is the case of zirconium cladding on nuclear fuel rods.<ref>{{cite journal |doi=10.1016/j.jnucmat.2019.02.042 |title=Hydrogen in zirconium alloys: A review |date=2019 |last1=Motta |first1=Arthur T. |last2=Capolungo |first2=Laurent |last3=Chen |first3=Long-Qing |last4=Cinbiz |first4=Mahmut Nedim |last5=Daymond |first5=Mark R. |last6=Koss |first6=Donald A. |last7=Lacroix |first7=Evrard |last8=Pastore |first8=Giovanni |last9=Simon |first9=Pierre-Clément A. |last10=Tonks |first10=Michael R. |last11=Wirth |first11=Brian D. |author11-link=Brian Wirth|last12=Zikry |first12=Mohammed A. |journal=Journal of Nuclear Materials |volume=518 |pages=440–460 |bibcode=2019JNuM..518..440M }}</ref>

===19th century===

By 1806 hydrogen was used to fill balloons.<ref>{{Cite journal |last=Szydło |first=Z. A. |date=2020 |title=Hydrogen - Some Historical Highlights |journal=Chemistry-Didactics-Ecology-Metrology |volume=25 |issue=1–2 |pages=5–34|doi=10.2478/cdem-2020-0001 |s2cid=231776282 |doi-access=free }}</ref>
[[François Isaac de Rivaz]] built the first [[de Rivaz engine]], an internal combustion engine powered by a mixture of hydrogen and oxygen in 1806. [[Edward Daniel Clarke]] invented the hydrogen gas blowpipe in 1819. The [[Döbereiner's lamp]] and [[limelight]] were invented in 1823. Hydrogen was [[Liquid hydrogen|liquefied]] for the first time by [[James Dewar]] in 1898 by using [[regenerative cooling]] and his invention, the [[vacuum flask]]. He produced [[solid hydrogen]] the next year.<ref name="nbb" />

One of the first [[quantum mechanics|quantum]] effects to be explicitly noticed (but not understood at the time) was [[James Clerk Maxwell]]'s observation that the [[specific heat capacity]] of {{chem2|H2}} unaccountably departs from that of a [[diatomic]] gas below room temperature and begins to increasingly resemble that of a monatomic gas at cryogenic temperatures. According to quantum theory, this behavior arises from the spacing of the (quantized) rotational energy levels, which are particularly wide-spaced in {{chem2|H2}} because of its low mass. These widely spaced levels inhibit equal partition of heat energy into rotational motion in hydrogen at low temperatures. Diatomic gases composed of heavier atoms do not have such widely spaced levels and do not exhibit the same effect.<ref name="Berman">{{cite journal
|last1=Berman|first1=R.|last2=Cooke|first2=A. H.|last3=Hill|first3=R. W.
|title=Cryogenics|journal=Annual Review of Physical Chemistry
|date=1956|volume=7|pages=1–20
|doi=10.1146/annurev.pc.07.100156.000245|bibcode = 1956ARPC....7....1B }}</ref>

===20th century===
The existence of the [[hydride|hydride anion]] was suggested by [[Gilbert N. Lewis]] in 1916 for group 1 and 2 salt-like compounds.  In 1920, Moers electrolyzed molten [[lithium hydride]] (LiH), producing a [[Stoichiometry|stoichiometric]] quantity of hydrogen at the anode.<ref name="Moers">{{cite journal|last=Moers|first=K.|title=Investigations on the Salt Character of Lithium Hydride|journal=Zeitschrift für Anorganische und Allgemeine Chemie|date=1920|volume=113|issue=191|pages=179–228|doi=10.1002/zaac.19201130116|url=https://zenodo.org/record/1428170|access-date=24 August 2019|archive-url=https://web.archive.org/web/20190824162148/https://zenodo.org/record/1428170/files/article.pdf|archive-date=24 August 2019|url-status=live}}</ref>

[[File:Emission_spectrum-H_labeled.svg|thumb|Hydrogen emission spectrum lines in the four visible lines of the [[Balmer series]]|alt=A line spectrum showing black background with narrow lines superimposed on it: one violet, one blue, one cyan, and one red.]]
Because of its simple atomic structure, consisting only of a proton and an electron, the [[hydrogen atom]], together with the spectrum of light produced from it or absorbed by it, has been central to the [[History of atomic theory|development of the theory of atomic structure]].<ref>{{cite book |last=Crepeau |first=R.
|title=Niels Bohr: The Atomic Model |series=Great Scientific Minds
|date=1 January 2006 |isbn=978-1-4298-0723-4
}}</ref> The energy levels of hydrogen can be calculated fairly accurately using the [[Bohr model]] of the atom, in which the electron "orbits" the proton, like how Earth orbits the Sun. However, the electron and proton are held together by electrostatic attraction, while planets and celestial objects are held by [[gravity]]. Due to the discretization of [[angular momentum]] postulated in early [[quantum mechanics]] by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, and therefore only certain allowed energies.<ref>{{cite web
|last=Stern
|first=D. P.
|date=16 May 2005
|url=http://www.iki.rssi.ru/mirrors/stern/stargaze/Q5.htm
|title=The Atomic Nucleus and Bohr's Early Model of the Atom
|publisher=NASA Goddard Space Flight Center (mirror)
|access-date=20 December 2007
|archive-url=https://web.archive.org/web/20081017073826/http://www.iki.rssi.ru/mirrors/stern/stargaze/Q5.htm
|archive-date=17 October 2008
}}</ref>

Hydrogen's unique position as the only neutral atom for which the [[Schrödinger equation]] can be directly solved, has significantly contributed to the understanding of quantum mechanics through the exploration of its energetics.<ref name="Laursen04">{{cite web|last1=Laursen|first1=S.|last2=Chang|first2=J.|last3=Medlin|first3=W.|last4=Gürmen|first4=N.|last5=Fogler|first5=H. S.|title=An extremely brief introduction to computational quantum chemistry|url=http://www.umich.edu/~elements/5e/web_mod/quantum/introduction_3.htm|website=Molecular Modeling in Chemical Engineering|publisher=University of Michigan|access-date=4 May 2015|date=27 July 2004|archive-url=https://web.archive.org/web/20150520061846/http://www.umich.edu/~elements/5e/web_mod/quantum/introduction_3.htm|archive-date=20 May 2015|url-status=live}}</ref> Furthermore, study of the corresponding simplicity of the hydrogen molecule and the corresponding cation [[H2+|{{chem2|H2+}}]] brought understanding of the nature of the chemical bond, which followed shortly after the quantum mechanical treatment of the hydrogen atom had been developed in the mid-1920s.<ref>{{Cite journal |last=Wilson |first=E. Bright |date=1977 |title=Impact of the Heitler-London hydrogen molecule paper on chemistry |url=https://onlinelibrary.wiley.com/doi/10.1002/qua.560120807 |journal=International Journal of Quantum Chemistry |language=en |volume=12 |issue=S11 |pages=17–28 |doi=10.1002/qua.560120807 |issn=1097-461X}}</ref>

==== Hydrogen-lifted airship ====
[[File:Hindenburg over New York 1937 (cropped).jpg|alt=Airship Hindenburg over New York|thumb|The [[Hindenburg-class airship|Hindenburg]] over [[New York City]] in 1937]]
Because {{chem2|H2}} is only 7% the density of air, it was once widely used as a [[lifting gas]] in balloons and [[airship]]s.<ref name="Almqvist03">{{cite book |last1=Almqvist |first1=Ebbe |url={{Google books|OI0fTJhydh4C|page=|keywords=|text=|plainurl=yes}} |title=History of industrial gases |date=2003 |publisher=Kluwer Academic/Plenum Publishers |isbn=978-0-306-47277-0 |location=New York, N.Y. |pages=47–56 |access-date=20 May 2015}}</ref> The first hydrogen-filled [[balloon]] was invented by [[Jacques Charles]] in 1783. Hydrogen provided the lift for the first reliable form of air-travel following the 1852 invention of the first hydrogen-lifted [[airship]] by [[Henri Giffard]]. German count [[Ferdinand von Zeppelin]] promoted the idea of rigid airships lifted by hydrogen that later were called [[Zeppelin]]s; the first of which had its maiden flight in 1900.<ref name="nbb" /> Regularly scheduled flights started in 1910 and by the outbreak of World War I in August 1914, they had carried 35,000 passengers without a serious incident. Hydrogen-lifted airships in the form of [[blimps]] were used as observation platforms and bombers during the War II, especially on the US Eastern seaboard.<ref>{{Cite web |last=Kratz |first=Jessie |date=2017-10-27 |title=Beyond the Hindenburg: Airships Throughout History |url=https://prologue.blogs.archives.gov/2017/10/27/beyond-the-hindenburg-airships-throughout-history/ |access-date=2025-04-09 |website=Pieces of History |language=en-US}}</ref>

The first non-stop transatlantic crossing was made by the British airship ''[[R34 (airship)|R34]]'' in 1919 and  regular passenger service resumed in the 1920s. Hydrogen was used in the [[LZ 129 Hindenburg|''Hindenburg'']] airship, which caught fire over [[New Jersey]] on 6 May 1937.<ref name="nbb" />  The hydrogen that filled the airship was ignited, possibly by static electricity, and burst into flames.<ref>{{Cite web |last=Follows |first=Mike |date=July 2, 2015 |title=What ignited the Hindenburg? |url=https://edu.rsc.org/feature/what-ignited-the-hindenburg/2000137.article |access-date=2025-02-19 |website=RSC Education |language=en}}</ref> Following this [[Hindenburg disaster]], commercial hydrogen airship travel [[Rigid airship#Demise|ceased]]. Hydrogen is still used, in preference to non-flammable but more expensive [[helium]], as a lifting gas for [[Weather balloon#Materials and equipment|weather balloons]].<ref>{{Cite web |last=Rappe |first=Mollie |date=May 9, 2023 |title=Researchers switch from helium to hydrogen weather balloons |url=https://phys.org/news/2023-05-helium-hydrogen-weather-balloons.html |access-date=2025-02-19 |website=phys.org |language=en}}</ref>

==== Deuterium and tritium ====
[[Deuterium]] was discovered in December 1931 by [[Harold Urey]], and [[tritium]] was prepared in 1934 by [[Ernest Rutherford]], [[Mark Oliphant]], and [[Paul Harteck]].<ref name="Nostrand" /> [[Heavy water]], which consists of deuterium in the place of regular hydrogen, was discovered by Urey's group in 1932.<ref name="nbb" />