Template:Infobox helium/sandbox

Helium, ₀₀He
Helium
Pronunciation	/ˈhiːliəm/ (HEE-lee-əm)
Appearance	colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field
Standard atomic weight Ar°(He)
	4.002602±0.000002; 4.0026±0.0001 (abridged);
Helium in the periodic table
	hydrogen ← helium → lithium
Group	group 18 (noble gases)
Period	period 1
Block	s-block
Electron configuration	1s2
Electrons per shell	2
Physical properties
Phase at STP	gas
Melting point	0.95 K (−272.20 °C, −457.96 °F) (at 2.5 MPa)
Boiling point	4.222 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 point	2.177 K, 5.043 kPa
Critical point	5.1953 K, 0.22746 MPa
Heat of fusion	0.0138 kJ/mol
Heat of vaporization	0.0829 kJ/mol
Molar heat capacity	5R/2 = 20.786 J/(mol·K)
Atomic properties
Oxidation states	common: (none);
Electronegativity	Pauling scale: no data
Ionization energies	1st: 2372.3 kJ/mol ; 2nd: 5250.5 kJ/mol ; ;
Covalent radius	28 pm
Van der Waals radius	140 pm
	Spectral lines of helium
Other properties
Natural occurrence	primordial
Crystal structure	hexagonal close-packed (hcp)
Thermal conductivity	0.1513 W/(m⋅K)
Magnetic ordering	diamagnetic
Speed of sound	972 m/s
CAS Number	7440-59-7
History
Discovery	1868
First isolation	William Ramsay, Per Teodor Cleve, Abraham Langlet (1895)
Isotopes of helium v; e;
	Category: Helium; view; talk; edit; \| references

References

^ "Standard Atomic Weights: Helium". CIAAW. 1983.
^ 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.
^ Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81st edition, CRC press.
^ 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.
^ Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.

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