Helium (He)

From Wikipedia, the free encyclopediaHelium 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.

Helium in the periodic table

SymbolHe
Atomic number2
Group18
Period1
Blocks
Element categoryNoble Gas

Physical properties

Phase at STPGas
Density0.1786 g/cm3
Atomic weight4.0026 u
Melting point0.95 K
-272.2 °C
-457.96 °F
Boiling point4.222 K
-268.928 °C
-452.0704 °F

Atomära egenskaper

Electronegativity (Pauling Scale)
Electron affinity-48 kJ/mol
Ionization energies
12372.3 kJ/mol
2 5250.5 kJ/mol

Electron configuration

Electron configuration1s2
Electrons per shell2

History

Discovered1868
Discovered byPierre Janssen
Norman Lockyer