Periodic Table of Elements




Helium was first discovered in the Sun. French astronomer Pierre Janssen in 1868 found proof that a new element existed in the Sun. He called the element helium. Helium was isolated by Sir William Ramsay and independently by N. A. Langley and P. T. Cleve at 1895 in London, England and Uppsala, Sweden.

Name: Helium
Symbol: He
Atomic number: 2
Atomic weight: 4.0026
State: gas
Group, period, block: 18, 1, s
Color: Colorless
Classification: noble gases
Electron configuration: 1s2

Physical Properties

Density: 214 kg m-3, 0.1786 g/L (0 C, 101.325 kPa)
Melting point: (under pressure) 0.95 K, -272.20 C,
-457.96 F
Boiling point: 4.22 K, -268.93 C, -452.07 F

Atomic Properties

Oxidation states: 0
Electronegativity: no data (Pauling scale)
Ionization energies: 1st: 2372.3 kJmol-1
Covalent radius: 28 pm
Van der Waals radius: 140 pm
  • He
  • Electron Configuration


There are two isotopes of Helium, 3He, and 4He.

Helium-4, the most common isotope is produced on Earth.

Helium-3 is present on Earth only in trace amounts.