Helium,  2He
Helium discharge tube.jpg
General properties
Pronunciationm/ (HEE-lee-əm)
Appearancecolorless gas, exhibiting a red-orange glow when placed in an electric field
Standard atomic weight (Ar, standard)4.002602(2)[1]
Helium in the periodic table
CaesiumBariumLanthanumCeriumPraseodymiumNeodymiumPromethiumSamariumEuropiumGadoliniumTerbiumDysprosiumHolmiumErbiumThuliumYtterbiumLutetiumHafniumTantalumTungstenRheniumOsmiumIridiumPlatinumGoldMercury (element)ThalliumLeadBismuthPoloniumAstatineRadon


Atomic number (Z)2
Groupgroup 18 (noble gases)
Periodperiod 1
Element category  noble gas
Electron configuration1s2
Electrons per shell
Physical properties
Phase at STPgas
Melting point0.95 K ​(−272.20 °C, ​−457.96 °F) (at 2.5 MPa)
Boiling point4.222 K ​(−268.928 °C, ​−452.070 °F)
Density (at STP)0.1786 g/L
when liquid (at m.p.)0.145 g/cm3
when liquid (at b.p.)0.125 g/cm3
Triple point2.177 K, ​5.043 kPa
Critical point5.1953 K, 0.22746 MPa
Heat of fusion0.0138 kJ/mol
Heat of vaporization0.0829 kJ/mol
Molar heat capacity20.78 J/(mol·K)[2]
Vapor pressure (defined by ITS-90)
P (Pa)1101001 k10 k100 k
at T (K)  1.231.672.484.21
Atomic properties
Oxidation states0
ElectronegativityPauling scale: no data
Ionization energies
  • 1st: 2372.3 kJ/mol
  • 2nd: 5250.5 kJ/mol
Covalent radius28 pm
Van der Waals radius140 pm
Color lines in a spectral range
Spectral lines of helium
Other properties
Crystal structurehexagonal close-packed (hcp)
Hexagonal close-packed crystal structure for helium
Speed of sound972 m/s
Thermal conductivity0.1513 W/(m·K)
Magnetic orderingdiamagnetic[3]
Magnetic susceptibility−1.88·10−6 cm3/mol (298 K)[4]
CAS Number7440-59-7
Namingafter Helios, Greek Titan of the Sun
DiscoveryPierre Janssen, Norman Lockyer (1868)
First isolationWilliam Ramsay, Per Teodor Cleve, Abraham Langlet (1895)
Main isotopes of helium
Iso­topeAbun­danceHalf-life (t1/2)Decay modePro­duct
| references

Helium (from Greek: ἥλιος, translit. Helios, lit. 'Sun') is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements. After hydrogen, helium is the second lightest and second most abundant element in the observable universe, being present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Its abundance is similar to this figure in the Sun and in Jupiter. This is due to the very high nuclear binding energy (per nucleon) of helium-4 with respect to the next three elements after helium. This helium-4 binding energy also accounts for why it is a product of both nuclear fusion and radioactive decay. Most helium in the universe is helium-4, the vast majority of which was formed during the Big Bang. Large amounts of new helium are being created by nuclear fusion of hydrogen in stars.

Helium is named for the Greek Titan of the Sun, Helios. It was first detected as an unknown yellow spectral line signature in sunlight during a solar eclipse in 1868 by Georges Rayet,[5] Captain C. T. Haig,[6] Norman R. Pogson,[7] and Lieutenant John Herschel,[8] and was subsequently confirmed by French astronomer Jules Janssen.[9] Janssen is often jointly credited with detecting the element along with Norman Lockyer. Janssen recorded the helium spectral line during the solar eclipse of 1868 while Lockyer observed it from Britain. Lockyer was the first to propose that the line was due to a new element, which he named. The formal discovery of the element was made in 1895 by two Swedish chemists, Per Teodor Cleve and Nils Abraham Langlet, who found helium emanating from the uranium ore cleveite. In 1903, large reserves of helium were found in natural gas fields in parts of the United States, which is by far the largest supplier of the gas today.

Liquid helium is used in cryogenics (its largest single use, absorbing about a quarter of production), particularly in the cooling of superconducting magnets, with the main commercial application being in MRI scanners. Helium's other industrial uses—as a pressurizing and purge gas, as a protective atmosphere for arc welding and in processes such as growing crystals to make silicon wafers—account for half of the gas produced. A well-known but minor use is as a lifting gas in balloons and airships.[10] As with any gas whose density differs from that of air, inhaling a small volume of helium temporarily changes the timbre and quality of the human voice. In scientific research, the behavior of the two fluid phases of helium-4 (helium I and helium II) is important to researchers studying quantum mechanics (in particular the property of superfluidity) and to those looking at the phenomena, such as superconductivity, produced in matter near absolute zero.

On Earth it is relatively rare—5.2 ppm by volume in the atmosphere. Most terrestrial helium present today is created by the natural radioactive decay of heavy radioactive elements (thorium and uranium, although there are other examples), as the alpha particles emitted by such decays consist of helium-4 nuclei. This radiogenic helium is trapped with natural gas in concentrations as great as 7% by volume, from which it is extracted commercially by a low-temperature separation process called fractional distillation. Previously, terrestrial helium—a non-renewable resource, because once released into the atmosphere it readily escapes into space—was thought to be in increasingly short supply.[11][12][13] However, recent studies suggest that helium produced deep in the earth by radioactive decay can collect in natural gas reserves in larger than expected quantities,[14][15] in some cases having been released by volcanic activity.[16]


Scientific discoveries

The first evidence of helium was observed on August 18, 1868, as a bright yellow line with a wavelength of 587.49 nanometers in the spectrum of the chromosphere of the Sun. The line was detected by French astronomer Jules Janssen during a total solar eclipse in Guntur, India.[17][18] This line was initially assumed to be sodium. On October 20 of the same year, English astronomer Norman Lockyer observed a yellow line in the solar spectrum, which he named the D3 because it was near the known D1 and D2 Fraunhofer line lines of sodium.[19][20] He concluded that it was caused by an element in the Sun unknown on Earth. Lockyer and English chemist Edward Frankland named the element with the Greek word for the Sun, ἥλιος (helios).[21][22]

Picture of visible spectrum with superimposed sharp yellow and blue and violet lines.
Spectral lines of helium

In 1881, Italian physicist Luigi Palmieri detected helium on Earth for the first time through its D3 spectral line, when he analyzed a material that had been sublimated during a recent eruption of Mount Vesuvius.[23]

Sir William Ramsay, the discoverer of terrestrial helium
The cleveite sample from which Ramsay first purified helium.[24]

On March 26, 1895, Scottish chemist Sir William Ramsay isolated helium on Earth by treating the mineral cleveite (a variety of uraninite with at least 10% rare earth elements) with mineral acids. Ramsay was looking for argon but, after separating nitrogen and oxygen from the gas liberated by sulfuric acid, he noticed a bright yellow line that matched the D3 line observed in the spectrum of the Sun.[20][25][26][27] These samples were identified as helium by Lockyer and British physicist William Crookes.[28][29] It was independently isolated from cleveite in the same year by chemists Per Teodor Cleve and Abraham Langlet in Uppsala, Sweden, who collected enough of the gas to accurately determine its atomic weight.[18][30][31] Helium was also isolated by the American geochemist William Francis Hillebrand prior to Ramsay's discovery when he noticed unusual spectral lines while testing a sample of the mineral uraninite. Hillebrand, however, attributed the lines to nitrogen.[32] His letter of congratulations to Ramsay offers an interesting case of discovery and near-discovery in science.[33]

In 1907, Ernest Rutherford and Thomas Royds demonstrated that alpha particles are helium nuclei by allowing the particles to penetrate the thin glass wall of an evacuated tube, then creating a discharge in the tube to study the spectrum of the new gas inside.[34] In 1908, helium was first liquefied by Dutch physicist Heike Kamerlingh Onnes by cooling the gas to less than one kelvin.[35][36] He tried to solidify it by further reducing the temperature but failed because helium does not solidify at atmospheric pressure. Onnes' student Willem Hendrik Keesom was eventually able to solidify 1 cm3 of helium in 1926 by applying additional external pressure.[37][38]

In 1913, Niels Bohr published his "trilogy"[39][40] on atomic structure that included a reconsideration of the Pickering–Fowler series as central evidence in support of his model of the atom.[41][42] This series is named for Edward Charles Pickering, who in 1896 published observations of previously unknown lines in the spectrum of the star ζ Puppis[43] (these are now known to occur with Wolf–Rayet and other hot stars).[44] Pickering attributed the observation (lines at 4551, 5411, and 10123 Å) to a new form of hydrogen with half-integer transition levels.[45][46] In 1912, Alfred Fowler[47] managed to produce similar lines from a hydrogen-helium mixture, and supported Pickering's conclusion as to their origin.[48] Bohr's model does not allow for half-integer transitions (nor does quantum mechanics) and Bohr concluded that Pickering and Fowler were wrong, and instead assigned these spectral lines to ionised helium, He+.[49] Fowler was initially skeptical[50] but was ultimately convinced[51] that Bohr was correct,[39] and by 1915 "spectroscopists had transferred [the Pickering–Fowler series] definitively [from hydrogen] to helium."[42][52] Bohr's theoretical work on the Pickering series had demonstrated the need for "a re-examination of problems that seemed already to have been solved within classical theories" and provided important confirmation for his atomic theory.[42]

In 1938, Russian physicist Pyotr Leonidovich Kapitsa discovered that helium-4 has almost no viscosity at temperatures near absolute zero, a phenomenon now called superfluidity.[53] This phenomenon is related to Bose–Einstein condensation. In 1972, the same phenomenon was observed in helium-3, but at temperatures much closer to absolute zero, by American physicists Douglas D. Osheroff, David M. Lee, and Robert C. Richardson. The phenomenon in helium-3 is thought to be related to pairing of helium-3 fermions to make bosons, in analogy to Cooper pairs of electrons producing superconductivity.[54]

Extraction and use

Historical marker, denoting a massive helium find near Dexter, Kansas

After an oil drilling operation in 1903 in Dexter, Kansas, produced a gas geyser that would not burn, Kansas state geologist Erasmus Haworth collected samples of the escaping gas and took them back to the University of Kansas at Lawrence where, with the help of chemists Hamilton Cady and David McFarland, he discovered that the gas consisted of, by volume, 72% nitrogen, 15% methane (a combustible percentage only with sufficient oxygen), 1% hydrogen, and 12% an unidentifiable gas.[18][55] With further analysis, Cady and McFarland discovered that 1.84% of the gas sample was helium.[56][57] This showed that despite its overall rarity on Earth, helium was concentrated in large quantities under the American Great Plains, available for extraction as a byproduct of natural gas.[58]

This enabled the United States to become the world's leading supplier of helium. Following a suggestion by Sir Richard Threlfall, the United States Navy sponsored three small experimental helium plants during World War I. The goal was to supply barrage balloons with the non-flammable, lighter-than-air gas. A total of 5,700 m3 (200,000 cu ft) of 92% helium was produced in the program even though less than a cubic meter of the gas had previously been obtained.[20] Some of this gas was used in the world's first helium-filled airship, the U.S. Navy's C-7, which flew its maiden voyage from Hampton Roads, Virginia, to Bolling Field in Washington, D.C., on December 1, 1921,[59] nearly two years before the Navy's first rigid helium-filled airship, the Naval Aircraft Factory-built USS Shenandoah, flew in September 1923.

Although the extraction process, using low-temperature gas liquefaction, was not developed in time to be significant during World War I, production continued. Helium was primarily used as a lifting gas in lighter-than-air craft. During World War II, the demand increased for helium for lifting gas and for shielded arc welding. The helium mass spectrometer was also vital in the atomic bomb Manhattan Project.[60]

The government of the United States set up the National Helium Reserve in 1925 at Amarillo, Texas, with the goal of supplying military airships in time of war and commercial airships in peacetime.[20] Because of the Helium Act of 1925, which banned the export of scarce helium on which the US then had a production monopoly, together with the prohibitive cost of the gas, the Hindenburg, like all German Zeppelins, was forced to use hydrogen as the lift gas. The helium market after World War II was depressed but the reserve was expanded in the 1950s to ensure a supply of liquid helium as a coolant to create oxygen/hydrogen rocket fuel (among other uses) during the Space Race and Cold War. Helium use in the United States in 1965 was more than eight times the peak wartime consumption.[61]

After the "Helium Acts Amendments of 1960" (Public Law 86–777), the U.S. Bureau of Mines arranged for five private plants to recover helium from natural gas. For this helium conservation program, the Bureau built a 425-mile (684 km) pipeline from Bushton, Kansas, to connect those plants with the government's partially depleted Cliffside gas field near Amarillo, Texas. This helium-nitrogen mixture was injected and stored in the Cliffside gas field until needed, at which time it was further purified.[62]

By 1995, a billion cubic meters of the gas had been collected and the reserve was US$1.4 billion in debt, prompting the Congress of the United States in 1996 to phase out the reserve.[18][63] The resulting Helium Privatization Act of 1996[64] (Public Law 104–273) directed the United States Department of the Interior to empty the reserve, with sales starting by 2005.[65]

Helium produced between 1930 and 1945 was about 98.3% pure (2% nitrogen), which was adequate for airships. In 1945, a small amount of 99.9% helium was produced for welding use. By 1949, commercial quantities of Grade A 99.95% helium were available.[66]

For many years, the United States produced more than 90% of commercially usable helium in the world, while extraction plants in Canada, Poland, Russia, and other nations produced the remainder. In the mid-1990s, a new plant in Arzew, Algeria, producing 17 million cubic meters (600 million cubic feet) began operation, with enough production to cover all of Europe's demand. Meanwhile, by 2000, the consumption of helium within the U.S. had risen to more than 15 million kg per year.[67] In 2004–2006, additional plants in Ras Laffan, Qatar, and Skikda, Algeria were built. Algeria quickly became the second leading producer of helium.[68] Through this time, both helium consumption and the costs of producing helium increased.[69] From 2002 to 2007 helium prices doubled.[70]

As of 2012, the United States National Helium Reserve accounted for 30 percent of the world's helium.[71] The reserve was expected to run out of helium in 2018.[71] Despite that, a proposed bill in the United States Senate would allow the reserve to continue to sell the gas. Other large reserves were in the Hugoton in Kansas, United States, and nearby gas fields of Kansas and the panhandles of Texas and Oklahoma. New helium plants were scheduled to open in 2012 in Qatar, Russia, and the US state of Wyoming, but they were not expected to ease the shortage.[71]

In 2013, Qatar started up the world's largest helium unit,[72] although the 2017 Qatar diplomatic crisis severely affected helium production there.[73] 2014 was widely acknowledged to be a year of over-supply in the helium business, following years of renowned shortages.[74] Nasdaq reported (2015) that for Air Products, an international corporation that sells gases for industrial use, helium volumes remain under economic pressure due to feedstock supply constraints.[75]

Other Languages
Afrikaans: Helium
አማርኛ: ሒሊየም
العربية: هيليوم
aragonés: Helio
armãneashti: Heliu
অসমীয়া: হিলিয়াম
asturianu: Heliu
Avañe'ẽ: Tataveve
azərbaycanca: Helium
تۆرکجه: هلیوم
বাংলা: হিলিয়াম
Bân-lâm-gú: Helium
башҡортса: Гелий
беларуская: Гелій
беларуская (тарашкевіца)‎: Гель
भोजपुरी: हीलियम
български: Хелий
བོད་ཡིག: ཧེ་རླུང་།
bosanski: Helij
brezhoneg: Heliom
català: Heli
Чӑвашла: Гели
Cebuano: Helyo
čeština: Helium
chiShona: Helium
corsu: Eliu
Cymraeg: Heliwm
dansk: Helium
Deutsch: Helium
Diné bizaad: Níłchʼi ászólí
eesti: Heelium
Ελληνικά: Ήλιο
emiliàn e rumagnòl: Êli
español: Helio
Esperanto: Heliumo
euskara: Helio
فارسی: هلیوم
Fiji Hindi: Helium
føroyskt: Helium
français: Hélium
Frysk: Helium
furlan: Eli
Gaeilge: Héiliam
Gaelg: Hailium
Gàidhlig: Helium
galego: Helio
Gĩkũyũ: Helium
ગુજરાતી: હીલિયમ
客家語/Hak-kâ-ngî: Hoi
хальмг: Гелион
한국어: 헬륨
Hawaiʻi: Hiliuma
հայերեն: Հելիում
हिन्दी: हिलियम
hornjoserbsce: Helium
hrvatski: Helij
Ido: Helio
Ilokano: Helio
Bahasa Indonesia: Helium
interlingua: Helium
íslenska: Helín
italiano: Elio
עברית: הליום
Basa Jawa: Hèliyum
ಕನ್ನಡ: ಹೀಲಿಯಮ್
ქართული: ჰელიუმი
қазақша: Гелий
Kiswahili: Heli
коми: Гелий
Kreyòl ayisyen: Elyòm
kurdî: Helyûm
Кыргызча: Гелий
кырык мары: Гелий
Latina: Helium
latviešu: Hēlijs
Lëtzebuergesch: Helium
lietuvių: Helis
Ligure: Elio
Limburgs: Helium
lingála: Eliyúmu
Livvinkarjala: Helium
la .lojban.: solnavni
magyar: Hélium
македонски: Хелиум
മലയാളം: ഹീലിയം
Māori: Haumāmā
मराठी: हेलियम
مصرى: هيليوم
Bahasa Melayu: Helium
Mìng-dĕ̤ng-ngṳ̄: Hâi
монгол: Гели
မြန်မာဘာသာ: ဟီလီယမ်
Nāhuatl: Tōnatiuhyoh
Nederlands: Helium
नेपाली: हिलियम
नेपाल भाषा: हिलियम
日本語: ヘリウム
Nordfriisk: Heelium
norsk: Helium
norsk nynorsk: Helium
Novial: Helium
occitan: Èli
ଓଡ଼ିଆ: ହିଲିଅମ
oʻzbekcha/ўзбекча: Geliy
ਪੰਜਾਬੀ: ਹੀਲੀਅਮ
पालि: हेलियम
پنجابی: ہیلیم
Papiamentu: Helium
Patois: Iiliom
Перем Коми: Гелий
ភាសាខ្មែរ: អេល្យូម
Piemontèis: Elio
Plattdüütsch: Helium
Ποντιακά: Ήλιον
português: Hélio
Ripoarisch: Helium
română: Heliu
Runa Simi: Ilyu
русский: Гелий
саха тыла: Гелий
संस्कृतम्: हीलियम्
Scots: Helium
Seeltersk: Helium
shqip: Heliumi
sicilianu: Èliu
සිංහල: හීලියම්
Simple English: Helium
slovenčina: Hélium
slovenščina: Helij
словѣньскъ / ⰔⰎⰑⰂⰡⰐⰠⰔⰍⰟ: Илїѥ
Soomaaliga: Hiliyaam
کوردی: ھیلیۆم
српски / srpski: Хелијум
srpskohrvatski / српскохрватски: Helij
Basa Sunda: Hélium
suomi: Helium
svenska: Helium
Tagalog: Elyo
தமிழ்: ஈலியம்
татарча/tatarça: Гелий
తెలుగు: హీలియం
тоҷикӣ: Гелий
Türkçe: Helyum
тыва дыл: Гелий
українська: Гелій
اردو: ہیلیم
ئۇيغۇرچە / Uyghurche: گېلىي
vepsän kel’: Gelii
Tiếng Việt: Heli
West-Vlams: Helium
Winaray: Helyo
ייִדיש: העליום
Yorùbá: Hílíọ̀mù
žemaitėška: Helis
Kabɩyɛ: Heelim