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colorless gas, exhibitin a reid-orange glow when placed in a heich-voltage electric field

Spectral lines o helium
General properties
Name, seembol, nummer helium, He, 2
Pronunciation /ˈhliəm/ HEE-lee-əm
Element category noble gases
Group, period, block 18 (noble gases), 1, s
Staundart atomic wicht 4.002602(2)
Electron confeeguration 1s2
Electron shells of helium (2)
Namin efter Helios, Greek god o the Sun
Discovery Pierre Janssen, Norman Lockyer (1868)
First isolation William Ramsay, Per Teodor Cleve, Abraham Langlet (1895)
Physical properties
Phase gas
Density (0 °C, 101.325 kPa)
0.1786 g/L
Liquid density at m.p. 0.145 g·cm−3
Liquid density at b.p. 0.125 g·cm−3
Meltin pynt (at 2.5 MPa) 0.95 K, −272.20 °C, −457.96 °F
Boilin pynt 4.22 K, −268.93 °C, −452.07 °F
Creetical pynt 5.19 K, 0.227 MPa
Heat o fusion 0.0138 kJ·mol−1
Heat o vaporization 0.0829 kJ·mol−1
Molar heat capacity 5R/2 = 20.786 J·mol−1·K−1
Vapor pressure (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 no data (Pauling scale)
Ionization energies 1st: 2372.3 kJ·mol−1
2nd: 5250.5 kJ·mol−1
Covalent radius 28 pm
Van der Waals radius 140 pm
Crystal structure hexagonal close-packed
Helium has a hexagonal close-packed crystal structure
Magnetic orderin diamagnetic[1]
Thermal conductivity 0.1513 W·m−1·K−1
Speed o soond 972 m·s−1
CAS registry nummer 7440-59-7
Most stable isotopes
Main article: Isotopes o helium
iso NA hauf-life DM DE (MeV) DP
3He 0.000137%* 3He is stable wi 1 neutron
4He 99.999863%* 4He is stable wi 2 neutrons
*Atmospheric value, abundance mey differ elsewhaur.
· r

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 than 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), particularly 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 weldin an in processes such 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 scientific research, the behavior o the twa fluid phases o helium-4 (helium I an helium II), is important tae researchers studyin quantum mechanics (in particular the property o superfluidity) an tae those leukin at the phenomena, such 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, although thare are ither examples), as the alpha particles emitted bi such decays consist 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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