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Technical data for Helium

Click any property name to see plots of that property for all the elements.

Overview
NameHelium
SymbolHe
Atomic Number2
Atomic Weight4.002602
Density0.1785 g/l[note]
Melting PointN/A[note]
Boiling Point-268.93 °C

Thermal properties
PhaseGas
Melting PointN/A[note]
Boiling Point-268.93 °C
Absolute Melting PointN/A[note]
Absolute Boiling Point4.22 K
Critical Pressure0.227 MPa (2.24 Atm)
Critical Temperature5.19 K
Heat of Fusion0.02 kJ/mol
Heat of Vaporization0.083 kJ/mol
Heat of CombustionN/A
Specific Heat5193.1 J/(kg K)[note]
Adiabatic Index5/3
Neel PointN/A
Thermal Conductivity0.1513 W/(m K)
Thermal ExpansionN/A

Bulk physical properties
Density0.1785 g/l[note]
Density (Liquid)N/A
Molar Volume0.022424
Brinell HardnessN/A
Mohs HardnessN/A
Vickers HardnessN/A
Bulk ModulusN/A
Shear ModulusN/A
Young ModulusN/A
Poisson RatioN/A
Refractive Index1.000035
Speed of Sound970 m/s
Thermal Conductivity0.1513 W/(m K)
Thermal ExpansionN/A

Reactivity
Valence0
ElectronegativityN/A
ElectronAffinity0 kJ/mol
Ionization Energies
2372.3, 5250.5 kJ/mol

Health and Safety
Autoignition PointN/A
FlashpointN/A
Heat of CombustionN/A
DOT Hazard Class2.2
DOT Numbers1963
EU NumberN/A
NFPA Fire Rating0
NFPA HazardsN/A
NFPA Health Rating1
NFPA Reactivity Rating0
RTECS NumberRTECSMH6520000
NFPA LabelNFPA Label

Classifications
Alternate NamesNone
Names of AllotropesNone
Blockp
Group18
Period1
Electron Configuration1s2
ColorColorless
Discovery
1895 in Sweden and United Kingdom
Gas phaseMonoatomic
CAS NumberCAS7440-59-7
CID NumberCID23987
Gmelin NumberN/A
NSC NumberN/A
RTECS NumberRTECSMH6520000

Electrical properties
Electrical TypeN/A
Electrical ConductivityN/A
ResistivityN/A
Superconducting PointN/A

Magnetic properties
Magnetic TypeDiamagnetic
Curie PointN/A
Mass Magnetic Susceptibility-5.9×10-9
Molar Magnetic Susceptibility-2.36×10-11
Volume Magnetic Susceptibility-1.05×10-9

Abundances
% in Universe23%
% in Sun23%
% in MeteoritesN/A
% in Earth's Crust5.5×10-7%
% in Oceans7.2×10-10%
% in HumansN/A

Atomic dimensions and structure
Atomic Radius31 pm
Covalent Radius32 pm
Van der Waals Radius140 pm
Crystal StructureFace Centered Cubic
Lattice Angles
π/2, π/2, π/2
Lattice Constants
424.2, 424.2, 424.2 pm
Space Group NameFm_ 3m
Space Group Number225

Nuclear Properties
Half-LifeStable
LifetimeStable
Decay ModeN/A
Quantum Numbers1S0
Neutron Cross Section0.007
Neutron Mass Absorption1×10-5
Known Isotopes
3He, 4He, 5He, 6He, 7He, 8He, 9He, 10He
Stable Isotopes
3He, 4He
Isotopic Abundances
3He0.000137%
4He99.999863%


Notes on the properties of Helium:

Absolute Melting Point: Helium does not solidify at standard pressure.

Density: Density at 0° Celsius.

Melting Point: Helium does not solidify at standard pressure.

Specific Heat: Value given for gas phase.

Up to date, curated data provided by
Mathematica's ElementData function from Wolfram Research, Inc.

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