Template:Infobox_helium
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Helium, 2He
A clear tube with a red light emanating from it
Helium
Pronunciation/ˈhiːliəm/ ​(HEE-lee-əm)
Appearancecolorless gas, exhibiting a 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
hydrogen ← helium → lithium
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)
Specific heat capacity5191.625 J/(kg·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 statescommon: (none)
ElectronegativityPauling scale: no data
Ionization energies
  • 1st: 2372.3 kJ/mol
  • 2nd: 5250.5 kJ/mol
Atomic radiusempirical: 31 pm
Covalent radius28 pm
Van der Waals radius140 pm
Color lines in a spectral range
Spectral lines of helium
Other properties
Natural occurrenceprimordial
Crystal structure ​hexagonal 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
Isotope abun­dance half-life (t1/2) mode pro­duct
He 0.0002% stable
He 99.9998% stable
 Category: Helium
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