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 of He (Helium) Enhanced Bohr Model of He (Helium) Bohr Model: He (Helium) Orbital Diagram of He (Helium)

Properties

Atomic Radius
120 pm
Molar Volume
Covalent Radius
46 pm
Metallic Radius
Ionic Radius
Crystal Radius
Van der Waals Radius
140 pm
Density
0.000164 g/cm³
Energy
Proton Affinity
177.8 kJ/mol
Electron Affinity
Ionization Energy
24.587387936 eV/particle
Heat of Vaporization
0.08 kJ/mol
Heat of Fusion
Heat of Formation
Electrons
Electron Shells2
Valence Electrons0
Electron Configuration1s2
Oxidation States
Electronegativity
Electrophilicity
0.0674191963846371 eV/particle
Phases
PhaseGas
Gas PhaseMonoatomic
Boiling Point
4.222 K
Melting Point
Critical Pressure
0.22746 MPa
Critical Temperature
5.195 K
Triple Point
2.177 K
5.043 kPa
Visual
Color
Colorless
Appearancecolorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field
Refractive Index
1.000035
Thermodynamic Properties
Thermal Conductivity
0.152 W/(m K)
Thermal Expansion
Molar Heat Capacity
20.786 J/(mol K)
Specific Heat Capacity
5.193 J/(g⋅K)
Heat Capacity Ratio (Adiabatic Index)5/3
Electrical Properties
Type
Electrical Conductivity
Electrical Resistivity
Superconducting Point
Magnetism
Typediamagnetic
Magnetic Susceptibility (Mass)
-0.0000000059 m³/Kg
Magnetic Susceptibility (Molar)
-0.0000000000236 m³/mol
Magnetic Susceptibility (Volume)
-0.00000000105
Magnetic Ordering
Curie Point
Neel Point
Structure
Crystal StructureFace Centered Cubic (HEX)
Lattice Constant
3.57 Å
Lattice Anglesπ/2, π/2, π/2
Mechanical Properties
Hardness
Bulk Modulus
Shear Modulus
Young Modulus
Poisson Ratio
Speed of Sound
970 m/s
Classification
CategoryNoble gases, Noble gases
CAS GroupVIII
IUPAC GroupVIIIA
Glawe Number1
Mendeleev Number112
Pettifor Number1
Geochemical Classvolatile
Goldschmidt Classatmophile
Other
Gas Basicity
148.5 kJ/mol
Dipole Polarizability
1.38375 ± 0.00002 a₀
C6 Dispersion Coefficient
1.42 a₀
Allotropes
Neutron Cross Section
0.007
Neutron Mass Absorption
0.00001
Quantum Numbers1S0
Space Group225 (Fm_3m)

Isotopes of Helium

Stable Isotopes2
Unstable Isotopes6
Radioactive Isotopes6

3He

Abundance
0.0002 ± 0.0002
Relative Atomic Mass
3.01602932197 ± 0.00000000006 Da
Mass Number3
G-Factor
-4.25525062 ± 0.00000006
Half Life
Spin1/2
Quadrupole Moment
0
Discovery Year1934
Parity+

4He

Abundance
99.9998 ± 0.0002
Relative Atomic Mass
4.00260325413 ± 0.00000000016 Da
Mass Number4
G-Factor
0
Half Life
Spin0
Quadrupole Moment
0
Discovery Year1908
Parity+

5He

AbundanceRadioactive ☢️
Relative Atomic Mass
5.012057224 ± 0.00002147 Da
Mass Number5
G-Factor
Half Life
602 ± 22 ys
Spin3/2
Quadrupole Moment
Discovery Year1937
Parity-

5He Decay Modes
Decay ModeIntensity
n (neutron emission)100%

6He

AbundanceRadioactive ☢️
Relative Atomic Mass
6.018885889 ± 0.000000057 Da
Mass Number6
G-Factor
0
Half Life
806.92 ± 0.24 ms
Spin0
Quadrupole Moment
0
Discovery Year1936
Parity+

6He Decay Modes
Decay ModeIntensity
β (β decay)100%
β d (β-delayed deuteron emission)0.000278%

7He

AbundanceRadioactive ☢️
Relative Atomic Mass
7.027990652 ± 0.000008115 Da
Mass Number7
G-Factor
Half Life
2.51 ± 0.07 zs
Spin3/2
Quadrupole Moment
Discovery Year1967
Parity

7He Decay Modes
Decay ModeIntensity
n (neutron emission)100%

8He

AbundanceRadioactive ☢️
Relative Atomic Mass
8.033934388 ± 0.000000095 Da
Mass Number8
G-Factor
0
Half Life
119.5 ± 1.5 ms
Spin0
Quadrupole Moment
0
Discovery Year1965
Parity+

8He Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)16%
β t (β-delayed triton emission)0.9%

9He

AbundanceRadioactive ☢️
Relative Atomic Mass
9.043946414 ± 0.000050259 Da
Mass Number9
G-Factor
Half Life
2.5 ± 2.3 zs
Spin1/2
Quadrupole Moment
0
Discovery Year1987
Parity

9He Decay Modes
Decay ModeIntensity
n (neutron emission)100%

10He

AbundanceRadioactive ☢️
Relative Atomic Mass
10.052815306 ± 0.000099676 Da
Mass Number10
G-Factor
0
Half Life
260 ± 40 ys
Spin0
Quadrupole Moment
0
Discovery Year1994
Parity+

10He Decay Modes
Decay ModeIntensity
2n (2-neutron emission)100%

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
Etymology (Name Origin)Greek: hêlios (sun).
PronunciationHEE-li-em (English)
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).

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
23 %
Abundance in Universe
23 %

Nuclear Screening Constants

1s0.3125