2
He
Helium
4.0026022
Helium (He)
Noble GasGroup 18Period 1s-block-block
Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among all the elements.
Latin name: Helium
Atomic Number
2
Atomic Mass
4.0026022 g/mol
Phase (STP)
Gas
Electron Config.
1s²
General
SymbolHe
Atomic Number2
Atomic Mass4.0026022 g/mol
CategoryNoble Gas
Group18
Period1
Blocks-block
Electron Configuration1s²
Valence Electrons2
ColourColorless
Appearancecolorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field
CAS NumberCAS7440-59-7
Physical Properties
Phase (STP)Gas
Density0.0001786 g/cm³
Melting Point-272.20°C · -457.96°F · 0.95 K
Boiling Point-268.93°C · -452.07°F · 4.22 K
Atomic Properties
Atomic Radius31 pm
Ionization Energy2372 kJ/mol
Electromagnetic
Electrical TypeInsulator
Abundance
In Universe23.0000%
In Sun23.0000%
In Earth's Crust0.000055%
In Oceans0.0000000007%
In Humans0%
In Meteorites0.0001%
Discovery & History
Discovery Year1868
Discovered ByPierre Janssen
Isotopes of Helium
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| He-3 | 0.000134% | Stable | — |
| He-4 | 99.999866% | Stable | — |