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Helium,  2He
Helium discharge tube.jpg
General properties
Pronunciation/ˈhliəm/ (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
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
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) 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]
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
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
3He 0.0002% stable
4He 99.9998% stable
| references
Because it is very light, helium is the gas of choice to fill airships such as the Goodyear blimp

Helium is a chemical element. It has the chemical symbol He, atomic number 2, and atomic weight of about 4.002602. There are 9 isotopes of helium, only two of which are stable. These are 3He and 4He. 4He is by far the most common isotope.

Helium is called a noble gas, because it does not regularly mix with other chemicals and form new compounds. It has the lowest boiling point of all the elements. It is the second most common element in the universe, after hydrogen, and has no color or smell. However, helium has a red-orange glow when placed in an electric field. Helium does not usually react with anything else. Astronomers detected the presence of helium in 1868, when its spectrum was identified in light from the Sun.[5] This was before its discovery on Earth.

Helium is used to fill balloons and airships because its density is lighter than air. It does not burn, so is safe for that kind of use. It is also used in some kinds of light bulbs. People can breathe in helium: it makes their voices sound higher than it normally does. This is a joke, but is dangerous as if they breathe in too much, hypoxia can injure or kill them as they are not breathing normal air. Breathing too much helium can also cause long-term effects to vocal cords.

Helium is created through the process of nuclear fusion in the Sun, and in similar stars. During this process, four hydrogen atoms are fused together to form one helium atom. On Earth it is made by the natural radioactive decay of heavy radioactive elements like thorium and uranium, although there are other examples. The alpha particles emitted by such decays consist of helium-4 nuclei.

History[change | change source]

Helium was discovered by the French astronomer pierre Janssen on August 18, 1868, as a bright yellow line in the spectrum of the chromosphere of the Sun.[6][7] The line was thought to be sodium. On the same year, English astronomer, Norman Lockyer, also observed it and found that it was caused by a new element.[8][7][9] Lockyer and English chemist Edward Frankland named the element helium, from the Greek word for the Sun, ἥλιος (helios).[10][9]

Characteristics[change | change source]

Helium is the second least reactive noble gas after neon. It is the second least reactive of all elements.[11] It is chemically inert and monatomic in all standard conditions.[7] Helium is the least water-soluble monatomic gas.[12]

Uses[change | change source]

Helium is used as a shielding gas in growing silicon and germanium crystals, in making titanium and zirconium, and in gas chromatography, because it is inert.[13] Helium is used as a shielding gas in arc welding.[7]

Helium is mixed with oxygen and other gases for deep underwater diving because it does not cause nitrogen narcosis.

Helium is also used to condense hydrogen and oxygen to make rocket fuel. It is used to remove the fuel and oxidizer from ground support equipment before the rocket launches. It is used to cool liquid hydrogen in space vehicles before the rocket launches.[13]

Helium is used as a heat-transfer medium in some nuclear reactors that are cooled down by gas.[14] Helium is also used in some hard disk drives.[15] Helium at low temperatures is used in cryogenics.[16]

Supply[change | change source]

Helium has become rare on Earth. If it gets free into the air it leaves the planet. Unlike hydrogen, which reacts with oxygen to form water, helium is not reactive. It stays as a gas. For many years after the 1925 Helium Act, the USA collected helium in a National Helium Reserve. American helium comes from wells in the Great Plains area. At present, more helium is supplied by Qatar than by the USA.

Several research organisations have released statements on the scarcity and conservation of helium.[17][18] These organisations released policy recommendations as early as 1995 and as late as 2016 urging the United States government to store and conserve helium because of the natural limits to the helium supply and the unique nature of the element.[17][18] For researchers, helium is irreplaceable because it is essential for producing very low temperatures. Helium at low temperatures is used in cryogenics, and in certain cryogenics applications. Liquid helium is used to cool certain metals to the extremely low temperatures required for superconductivity, such as in superconducting magnets for magnetic resonance imaging.[18]

References[change | change source]

  1. Meija, J.; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
  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. Based on this location, its name was derived from the Greek word for Sun, helios.
  6. Kochhar, Rajesh (2013-04-04). "Natural history in India during the 18th and 19th centuries". Journal of Biosciences. 38 (2): 201–224. doi:10.1007/s12038-013-9316-9. ISSN 0250-5991.
  7. 7.0 7.1 7.2 7.3 Emsley, John. (2001). Nature's building blocks : an A-Z guide to the elements. Oxford: Oxford University Press. ISBN 0-19-850341-5. OCLC 46984609.
  8. "VIII. Notice of an observation of the spectrum of a solar prominence, by J. N. Lockyer, Esq., in a letter to the secretary. Communicated by Dr. Sharpey". Proceedings of the Royal Society of London. 17: 91–92. 1869-12-31. doi:10.1098/rspl.1868.0011. ISSN 0370-1662.
  9. 9.0 9.1 "helium | Origin and meaning of helium by Online Etymology Dictionary". www.etymonline.com. Retrieved 2020-09-19.
  10. "The British Association Meeting at Edinburgh". Nature. 4 (92): 261–278. 1871. doi:10.1038/004261a0. ISSN 0028-0836.
  11. Lewars, Errol. (2008). Modeling marvels : computational anticipation of novel molecules. [Dordrecht]: Springer. ISBN 978-1-4020-6973-4. OCLC 314371890.
  12. Weiss, Ray F. (1971). "Solubility of helium and neon in water and seawater". Journal of Chemical & Engineering Data. 16 (2): 235–241. doi:10.1021/je60049a019. ISSN 0021-9568.
  13. 13.0 13.1 CRC handbook of chemistry and physics. Lide, David R., 1928- (86th ed., 2005-2006 ed.). Boca Raton: CRC Press. 2005. ISBN 0-8493-0486-5. OCLC 61108810.CS1 maint: others (link)
  14. Van Nostrand's encyclopedia of chemistry. Considine, Glenn D., (5th edition ed.). Hoboken, NJ. ISBN 0-471-61525-0. OCLC 56111623.CS1 maint: extra punctuation (link) CS1 maint: others (link) CS1 maint: extra text (link)
  15. Gallagher, Sean (2013-11-04). "HGST balloons disk capacity with helium-filled 6TB drive". Ars Technica. Retrieved 2020-09-20.
  16. "Wayback Machine" (PDF). web.archive.org. 2011-07-06. Retrieved 2020-09-20.
  17. 17.0 17.1 American Physical Society (1995). “National Policy”. https://www.aps.org/policy/statements/95_3.cfm
  18. 18.0 18.1 18.2 Epple, Dennis (1982). "The Helium Storage Controversy: Modeling Natural Resource Supply: The complex issue of helium storage provides a case study of the difficult decisions involved in using natural resources". American Scientist.