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Helium,  2He
Helium discharge tube.jpg
General properties
Appearance colorless gas, exhibitin a reid-orange glow when placed in a heich-voltage electric field
Staundart atomic wecht (Ar, staundart) 4.002602(2)
Helium in the periodic cairt
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 Airn Cobalt Nickel Capper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Siller (element) 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 Mercur (element) Thallium Leid (element) 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 Ununtrium Flerovium Ununpentium Livermorium Ununseptium Ununoctium


Atomic nummer (Z) 2
Group group 18 (noble gases)
Period period 1
Element category   noble gas
Block s-block
Electron confeeguration 1s2
Electrons per shell
Pheesical properties
Phase (at STP) gas
Meltin pynt (at 2.5 MPa) 0.95 K ​(−272.20 °C, ​−457.96 °F)
Bylin pynt 4.22 K ​(−268.93 °C, ​−452.07 °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
Creetical pynt 5.19 K, 0.227 MPa
Heat o fusion 0.0138 kJ/mol
Heat o vapourisation 0.0829 kJ/mol
Molar heat capacity 5R/2 = 20.786 J/(mol·K)
Vapour pressur (defined bi 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 states 0
Electronegativity Pauling scale: no data
Covalent radius 28 pm
Van der Waals radius 140 pm
Color lines in a spectral range
Crestal structur hexagonal close-packed (hcp)
Hexagonal close-packed creestal structur for helium
Speed o soond 972 m/s
Thermal conductivity 0.1513 W/(m·K)
Magnetic orderin diamagnetic[1]
CAS Nummer 7440-59-7
Diskivery Pierre Janssen, Norman Lockyer (1868)
First isolation William Ramsay, Per Teodor Cleve, Abraham Langlet (1895)
Main isotopes o helium
Iso­tope Abun­dance Hauf-life (t1/2) Decay mode Pro­duct
3He 0.000137%* stable
4He 99.999863%* stable
  • Atmospheric value, abundance mey differ elsewhaur.
| references | in Wikidata

Helium is a chemical element wi seembol He an atomic nummer 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heids the noble gas group in the periodic table. Its boilin an meltin pynts are the lawest amang the elements an it exists anly as a gas except in extreme condeetions.

Helium is the seicont lichtest element an is the seicont maist abundant element in the observable universe, bein present at aboot 24% o the tot elemental mass, which is mair nor 12 times the mass o aw the hivier elements combined. Its abundance is seemilar tae this figure in the Sun an in Jupiter. This is due tae the very heich nuclear bindin energy (per nucleon) o helium-4 wi respect tae the next three elements efter helium. This helium-4 bindin energy an aa accoonts for why it is a product o baith nuclear fusion an radioactive decay. Maist helium in the universe is helium-4, an is believed tae hae been fairmed durin the Big Bang. Lairge amoonts o new helium are bein creatit bi nuclear fusion o hydrogen in starns.

Helium is named for the Greek God o the Sun, Helios. It wis first detectit as an unkent yellae spectral line signatur in sunlicht durin a solar eclipse in 1868 bi French astronomer Jules Janssen. Janssen is jyntly creditit wi detectin the element alang wi Norman Lockyer. Jannsen observed durin the solar eclipse o 1868 while Lockyer observed frae Breetain. Lockyer wis the first tae propose that the line wis due tae a new element, which he named. The formal discovery o the element wis made in 1895 bi twa Swadish chemists, Per Teodor Cleve an Nils Abraham Langlet, who foond helium emanatin frae the uranium ore cleveite. In 1903, lairge reserves o helium wur foond in naitural gas fields in pairts o the Unitit States, which is bi far the lairgest supplier o the gas the day.

Helium is uised in cryogenics (its lairgest single uise, absorbin aboot a quarter o production), parteecularly in the cuilin o superconductin magnets, wi the main commercial application bein in MRI scanners. Helium's ither industrial uises—as a pressurizin an purge gas, as a protective atmosphere for arc waldin an in processes sic as growin crystals tae mak silicon wafers—accoont for hauf o the gas produced. A well-kent but minor uise is as a liftin gas in balloons an airships.[2] As wi ony gas wi differin density frae air, inhalin a smaa volume o helium temporarily chynges the timbre an quality o the human vyce. In scienteefic research, the behaviour o the twa fluid phases o helium-4 (helium I an helium II), is important tae researchers studyin quantum mechanics (in parteecular the property o superfluidity) an tae those leukin at the phenomena, sic as superconductivity, that temperaturs near absolute zero produce in matter.

On Yird it is relatively rare—0.00052% bi volume in the atmosphere. Maist terrestrial helium present the day is creatit bi the naitural radioactive decay o hivy radioactive elements (thorium an uranium, awtho thare are ither examples), as the alpha particles emitted bi sic decays conseest o helium-4 nuclei. This radiogenic helium is trapped wi naitural gas in concentrations up tae 7% bi volume, frae which it is extractit commercially bi a law-temperatur separation process cried fractional distillation.

References[eedit | eedit soorce]

  1. Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81st edition, CRC press.
  2. Helium: Up, Up and Away? Melinda Rose, Photonics Spectra, Oct. 2008. Accessed Feb 27, 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.

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