chemical element with symbol He and atomic number 2; rare gas

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, 00He
Pronunciation/ˈhliəm/ (HEE-lee-əm)
Appearancecolorless gas, exhibiting a red-orange glow when placed in an electric field
Standard atomic weight Ar°(He)
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


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 Titan 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% stable
4He 99.9998% stable
 Category: Helium
| references
Because it is very light, helium is the gas of choice to fill airships such as the Goodyear blimp

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.[6] 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 may seem silly, but it can actually be quite 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

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.[7][8] 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][9][10] Lockyer and English chemist Edward Frankland named the element helium, from the Greek word for the Sun, ἥλιος (helios).[10][11]

Characteristics change

Helium is the second least reactive noble gas after neon. It is the second least reactive of all elements.[12] It is chemically inert and monatomic in all standard conditions.[8] Helium is the least water-soluble monatomic gas.[13]

Uses change

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.[14] Helium is used as a shielding gas in arc welding.[8]

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.[14]

Helium is used as a heat-transfer medium in some nuclear reactors that are cooled down by gas.[15] Helium is also used in some hard disk drives.[16] Helium at low temperatures is used in cryogenics.[17]

Supply change

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.

Helium-Neon Laser

Several research organisations have released statements on the scarcity and conservation of helium.[18][19] 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.[18][19] 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.[19]

References change

  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. Based on this location, its name was derived from the Greek word for Sun, helios.
  7. 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. PMID 23660654. S2CID 26271510. Archived from the original on 2022-05-26. Retrieved 2020-09-19.
  8. 8.0 8.1 8.2 8.3 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. Retrieved 2020-09-19.
  9. "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. Archived from the original on 2020-08-08. Retrieved 2020-09-19.
  10. 10.0 10.1 "helium | Origin and meaning of helium by Online Etymology Dictionary". www.etymonline.com. Archived from the original on 2020-08-27. Retrieved 2020-09-19.
  11. "The British Association Meeting at Edinburgh". Nature. 4 (92): 261–278. 1871. Bibcode:1871Natur...4..261.. doi:10.1038/004261a0. ISSN 0028-0836. S2CID 3963038. Archived from the original on 2020-05-08. Retrieved 2020-09-19.
  12. Lewars, Errol. (2008). Modeling marvels : computational anticipation of novel molecules. [Dordrecht]: Springer. ISBN 978-1-4020-6973-4. OCLC 314371890. Retrieved 2020-09-19.
  13. 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. Archived from the original on 2020-08-07. Retrieved 2020-09-19.
  14. 14.0 14.1 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.{{cite book}}: CS1 maint: others (link)
  15. {{Cite book|url=https://www.worldcat.org/oclc/56111623%7Ctitle=Van Nostrand's encyclopedia of chemistry.|others=Considine, Glenn D.|date=3 February 2005|isbn=0-471-61525-0|edition=5th|location=Hoboken, NJ|oclc=56111623|access-date=20 September 2020}
  16. Gallagher, Sean (2013-11-04). "HGST balloons disk capacity with helium-filled 6TB drive". Ars Technica. Archived from the original on 2017-07-07. Retrieved 2020-09-20.
  17. "LHC guide" (PDF). CERN. 2011-07-06. Archived from the original (PDF) on 2011-07-06. Retrieved 2020-09-20.
  18. 18.0 18.1 American Physical Society (1995). “National Policy”. https://www.aps.org/policy/statements/95_3.cfm Archived 2017-12-31 at the Wayback Machine
  19. 19.0 19.1 19.2 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.