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Chemical element with atomic number 2 (He)
Helium, 2He
A clear tube with a red light emanating from it
Helium
Pronunciation/ˈhliəm/ (HEE-lee-əm)
Appearancecolorless gas, "exhibiting 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)
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


He

Ne
hydrogenheliumlithium
Atomic number (Z)2
Groupgroup 18 (noble gases)
Periodperiod 1
Block  s-block
Electron configuration1s
Electrons per shell2
Physical properties
Phase at STPgas
Boiling point4.222 K ​(−268.928 °C, ​−452.070 °F)
Density (at STP)0.1786 g/L
when liquid (at b.p.)0.125 g/cm
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)
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
Thermal conductivity0.1513 W/(m⋅K)
Magnetic orderingdiamagnetic
Molar magnetic susceptibility−1.88×10 cm/mol (298 K)
Speed of sound972 m/s
CAS Number7440-59-7
History
Namingafter Helios, Greek god of the——Sun
DiscoveryNorman Lockyer (1868)
First isolationWilliam Ramsay, Per Teodor Cleve, Abraham Langlet (1895)
Isotopes of helium
Main isotopes Decay
abun­dance half-life (t1/2) mode pro­duct
He 0.0002% stable
He 99.9998% stable
 Category: Helium
| references
child table, as reused in {IB-He}
Main isotopes of helium
Main isotopes Decay
abun­dance half-life (t1/2) mode pro­duct
He 0.0002% stable
He 99.9998% stable
Data sets read by {{Infobox element}} Name and identifiers Symbol etymology (11 non-trivial) Top image (caption, alt) Pronunciation Allotropes (overview) Group (overview) Period (overview) Block (overview) Natural occurrence Phase at STP Oxidation states Spectral lines image Electron configuration (cmt, ref) Isotopes Standard atomic weight   most stable isotope Wikidata Wikidata * * Not used in {{Infobox element}} (2023-01-01)
See also {{Index of data sets}} · Cat:data sets (45) · (this table: )
References
These references will appear in the "article." But this list appears only on this page.
  1. ^ "Standard Atomic Weights: Helium". CIAAW. 1983.
  2. ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  3. ^ 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.
  4. ^ Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81st edition, CRC press.
  5. ^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
  6. ^ 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.

One of these is a named reference. It may be, cited in the containing article as

  • <ref name = "CIAAW2013" /> for the source Atomic weights of the elements 2013 (from subtemplates used by {{Infobox element}})

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