Helium

Helium (He)

Colourless, odourless gaseous nonmetallic element. Belongs to group 18 of the periodic table. Lowest boiling point of all elements and can only be solidified under pressure. Chemically inert, no known compounds. Discovered in the solar spectrum in 1868 by Lockyer.
Atomic Number2
Atomic Weight4.002602
Mass Number4
Group18
Period1
Blocks
Protons2 p+
Neutrons2 n0
Electrons2 e-
Helium discharge tube.jpg Animated Bohr Model Enhanced Bohr Model Bohr Model Orbital Diagram

Properties

Atomic Radius
120 pm
Atomic Volume
Covalent Radius
46 pm
Metallic Radius
Ionic Radius
Crystal Radius
Van der Waals radius
140 pm
Density
0.000164 g/cm³
Boiling Point
4.216 K
Melting Point
0.95 K
Electrons per shell2
Electronegativity
Electrophilicity
0.0674191963846 eV/particle
Proton Affinity
177.8 kJ/mol
Electron Affinity
Ionization Potential
24.587387936 eV/particle
Heat of Vaporization
0.08 kJ/mol
Heat of Fusion
Heat of Formation
Molar Heat Capacity
20.786 J/(mol K)
Specific Heat Capacity
5.193 J/(g⋅K)
Thermal Conductivity
0.152 W/(m K)
Gas Basicity
148.5 kJ/mol
Dipole Polarizability
1.38375 a₀
C6 Dispersion Coefficient
1.42 a₀
Oxidation States0
Color
Colorless
Crystal StructureFace Centered Cubic (HEX)
Lattice Constant
3.57 Å
Bulk Modulus
Electrical Resistivity
Electron Configuration1s2
Magnetic Ordering
Magnetic Susceptibility
PhaseGas
Poisson Ratio
Shear Modulus
Young's Modulus
Allotropes
Alternate Names
Adiabatic Index
Appearance
Electric Conductivity
Critical Pressure
Critical Temperature
Curie Point
Electrical
Hardness
Magnetic Susceptibility
Magnetic
Neel Point
Neutron Cross Section
Neutron Mass Absorption
Gas Phase
Quantum Numbers
Refractive Index
Space Group
Speed of Sound
Superconducting Point
Thermal Expansion
Valence Electrons
Classification
CategoryNoble gases, Noble gases
CAS GroupVIII
IUPAC GroupVIIIA
Glawe Number1
Mendeleev Number112
Pettifor Number1
Geochemical Classvolatile
Goldschmidt Classatmophile
Radioactivity
RadioactiveNo
Decay Mode
Half-Life
Lifetime
Abundance
Abundance in Earth's crust
0.008 mg/kg
Abundance in Oceans
0.000007 mg/L
Abundance in Human Body
Abundance in Meteor
Abundance in Sun
Abundance in Universe23%

Isotopes of Helium

Stable Isotopes
3He 4He
Unstable Isotopes
5He 6He 7He 8He 9He 10He

History

French astronomer Jules Janssen obtained the first evidence of helium during the solar eclipse of 1868. Norman Lockyer and Edward Frankland suggested the name helium for the new element. In 1895, Sir William Ramsay discovered helium in the uranium mineral cleveite. It was independently discovered in cleveite by Per Teodor Cleve and Abraham Langlet. From the Greek word helios, the sun

DiscoverersSir William Ramsey, Nils Langet, P.T.Cleve
Discovery LocationScotland/Sweden
Discovery Year1895
Name OriginGreek: hêlios (sun).
Helium is not known to be toxic
Unlike any other element, helium will remain liquid down to absolute zero at normal pressures

Uses

Helium is used as a protective gas in growing silicon and germanium crystals, in titanium and zirconium production, and in gas chromatography. Helium at low temperatures is used in cryogenics. Helium is used for filling balloons and for pressurizing liquid fuel rockets. Helium is used as a shielding gas in arc welding processes. Used in balloons, deep sea diving & welding. Also used in very low temperature research.

Sources

Found in natural gas deposits & in the air (5 parts per billion) Constantly lost to space; replenished by radioactive decay (alpha particles).