Helium, 2He
A clear tube with a red light emanating from it
Pronunciation/ˈhliəm/ (HEE-lee-əm)
Appearancecolorless gas, exhibiting a gray, cloudy glow (or reddish-orange if an especially high voltage is used) when placed in an electric field
Standard atomic weight Ar°(He)
  • 4.002602±0.000002
  • 4.0026±0.0001 (abridged)[1]
Helium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)2
Groupgroup 18 (noble gases)
Periodperiod 1
Block  s-block
Electron configuration1s2
Electrons per shell2
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) 1 10 100 1 k 10 k 100 k
at T (K)     1.23 1.67 2.48 4.21
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
Natural occurrenceprimordial
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]
Molar magnetic susceptibility−1.88×10−6 cm3/mol (298 K)[4]
CAS Number7440-59-7
Namingafter Helios, Greek god of the Sun
DiscoveryPierre Janssen, Norman Lockyer (1868)
First isolationWilliam Ramsay, Per Teodor Cleve, Abraham Langlet (1895)
Isotopes of helium
Main isotopes[5] Decay
abun­dance half-life (t1/2) mode pro­duct
3He 0.0002%
Preview warning: Infobox He isotopes: Abundance percentage not recognised "na=0.0002%" cat#%
4He 99.9998%
Preview warning: Infobox He isotopes: Abundance percentage not recognised "na=99.9998%" cat#%
 Category: Helium
| references

Helium (from Greek: ἥλιος, romanizedhelios, lit.'sun') is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table.[a] Its boiling point is the lowest among all the elements, and it does not have a melting point at standard pressure. It is the second-lightest and second most abundant element in the observable universe, after hydrogen. It is 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 in both the Sun and Jupiter, because of 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. The most common isotope of helium in the universe is helium-4, the vast majority of which was formed during the Big Bang. Large amounts of new helium are created by nuclear fusion of hydrogen in stars.

Helium was first detected as an unknown, yellow spectral line signature in sunlight during a solar eclipse in 1868 by Georges Rayet,[12] Captain C. T. Haig,[13] Norman R. Pogson,[14] and Lieutenant John Herschel,[15] and was subsequently confirmed by French astronomer Jules Janssen.[16] 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 after the sun. The formal discovery of the element was made in 1895 by chemists Sir William Ramsay, Per Teodor Cleve, and Nils Abraham Langlet, who found helium emanating from the uranium ore, cleveite, which is now not regarded as a separate mineral species, but as a variety of uraninite.[17][18] In 1903, large reserves of helium were found in natural gas fields in parts of the United States, by far the largest supplier of the gas today.

Liquid helium is used in cryogenics (its largest single use, consuming about a quarter of production), and in the cooling of superconducting magnets, with its main commercial application 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 crystal to make silicon wafers—account for half of the gas produced. A small but well-known use is as a lifting gas in balloons and airships.[19] 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. Terrestrial helium is a non-renewable resource because once released into the atmosphere, it promptly escapes into space. Its supply is thought to be rapidly diminishing.[20][21] However, some studies suggest that helium produced deep in the earth by radioactive decay can collect in natural gas reserves in larger-than-expected quantities,[22] in some cases having been released by volcanic activity.[23]

  1. ^ "Standard Atomic Weights: Helium". CIAAW. 1983.
  2. ^ Shuen-Chen Hwang, Robert D. Lein, Daniel A. Morgan (2005). "Noble Gases". Kirk Othmer Encyclopedia of Chemical Technology. Wiley. pp. 343–383. doi:10.1002/0471238961.0701190508230114.a01.
  3. ^ Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81st edition, CRC press.
  4. ^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
  5. ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  6. ^ Grochala, Wojciech (1 November 2017). "On the position of helium and neon in the Periodic Table of Elements". Foundations of Chemistry. 20 (2018): 191–207. doi:10.1007/s10698-017-9302-7.
  7. ^ Bent Weberg, Libby (18 January 2019). ""The" periodic table". Chemical & Engineering News. 97 (3). Retrieved 27 March 2020.
  8. ^ Grandinetti, Felice (23 April 2013). "Neon behind the signs". Nature Chemistry. 5 (2013): 438. Bibcode:2013NatCh...5..438G. doi:10.1038/nchem.1631. PMID 23609097.
  9. ^ Kurushkin, Mikhail (2020). "Helium's placement in the Periodic Table from a crystal structure viewpoint". IUCrJ. 7 (4): 577–578. doi:10.1107/S2052252520007769. PMC 7340260. PMID 32695406. Retrieved 19 June 2020.
  10. ^ Labarca, Martín; Srivaths, Akash (2016). "On the Placement of Hydrogen and Helium in the Periodic System: A New Approach". Bulgarian Journal of Science Education. 25 (4): 514–530. Archived from the original on 29 November 2021. Retrieved 19 June 2020.
  11. ^ Lewars, Errol G. (5 December 2008). Modeling Marvels: Computational Anticipation of Novel Molecules. Springer Science & Business Media. pp. 69–71. ISBN 978-1-4020-6973-4. Archived from the original on 19 May 2016.
  12. ^ Rayet, G. (1868) "Analyse spectral des protubérances observées, pendant l'éclipse totale de Soleil visible le 18 août 1868, à la presqu'île de Malacca" (Spectral analysis of the protuberances observed during the total solar eclipse, seen on 18 August 1868, from the Malacca peninsula), Comptes rendus ... , 67 : 757–759. From p. 758: " ... je vis immédiatement une série de neuf lignes brillantes qui ... me semblent devoir être assimilées aux lignes principales du spectre solaire, B, D, E, b, une ligne inconnue, F, et deux lignes du groupe G." ( ... I saw immediately a series of nine bright lines that ... seemed to me should be classed as the principal lines of the solar spectrum, B, D, E, b, an unknown line, F, and two lines of the group G.)
  13. ^ Captain C. T. Haig (1868) "Account of spectroscopic observations of the eclipse of the sun, August 18th, 1868" Proceedings of the Royal Society of London, 17 : 74–80. From p. 74: "I may state at once that I observed the spectra of two red flames close to each other, and in their spectra two broad bright bands quite sharply defined, one rose-madder and the other light golden."
  14. ^ Pogson filed his observations of the 1868 eclipse with the local Indian government, but his report wasn't published. (Biman B. Nath, The Story of Helium and the Birth of Astrophysics (New York, New York: Springer, 2013), p. 8.) Nevertheless, Lockyer quoted from his report. From p. 320 Archived 17 August 2018 at the Wayback Machine of Lockyer, J. Norman (1896) "The story of helium. Prologue," Nature, 53 : 319–322 : "Pogson, in referring to the eclipse of 1868, said that the yellow line was "at D, or near D." "
  15. ^ Lieutenant John Herschel (1868) "Account of the solar eclipse of 1868, as seen at Jamkandi in the Bombay Presidency," Proceedings of the Royal Society of London, 17 : 104–120. From p. 113: As the moment of the total solar eclipse approached, " … I recorded an increasing brilliancy in the spectrum in the neighborhood of D, so great in fact as to prevent any measurement of that line till an opportune cloud moderated the light. I am not prepared to offer any explanation of this." From p. 117: "I also consider that there can be no question that the ORANGE LINE was identical with D, so far as the capacity of the instrument to establish any such identity is concerned."
  16. ^ In his initial report to the French Academy of Sciences about the 1868 eclipse, Janssen made no mention of a yellow line in the solar spectrum. See: However, subsequently, in an unpublished letter of 19 December 1868 to Charles Sainte-Claire Deville, Janssen asked Deville to inform the French Academy of Sciences that : "Several observers have claimed the bright D line as forming part of the spectrum of the prominences on 18 August. The bright yellow line did indeed lie very close to D, but the light was more refrangible [i.e., of shorter wavelength] than those of the D lines. My subsequent studies of the Sun have shown the accuracy of what I state here." (See: (Launay, 2012), p. 45.)
  17. ^ "Cleveite". Mindat.org. Retrieved 14 February 2020.
  18. ^ "Uraninite". Mindat.org. Retrieved 14 February 2020.
  19. ^ Rose, Melinda (October 2008). "Helium: Up, Up and Away?". Photonics Spectra. Archived from the original on 22 August 2010. Retrieved 27 February 2010. For a more authoritative but older 1996 pie chart showing U.S. helium use by sector, showing much the same result, see the chart reproduced in "Applications" section of this article.
  20. ^ Connor, Steve (23 August 2010). "Why the world is running out of helium". The Independent. London. Archived from the original on 27 September 2013. Retrieved 16 September 2013.
  21. ^ Siegel, Ethan (12 December 2012). "Why the World Will Run Out of Helium". Starts with a Bang. Scienceblogs.com. Archived from the original on 14 September 2013. Retrieved 16 September 2013.
  22. ^ Szondy, David (24 August 2015). "We may not be running out of helium after all". www.gizmag.com. Archived from the original on 25 March 2016. Retrieved 1 April 2016.
  23. ^ Sample, Ian (28 June 2016). "Huge helium gas find in east Africa averts medical shortage". The Guardian. Archived from the original on 29 June 2016. Retrieved 29 June 2016.

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