Helium

Koushik 26/06/2026 19:58:08 Updated 26/06/2026 19:58:08

Property	Value
Atomic Number	2
Element	Helium
Symbol	He
Atomic Mass	4.0026 u
Number of Neutrons	2 (most common isotope)
Number of Protons	2
Number of Electrons	2
Period	1
Group	18
Phase	Gas
Radioactive	No
Natural	Yes
Metal	No
Nonmetal	Yes
Metalloid	No
Type	Noble Gas
Atomic Radius	31 pm
Electronegativity	Not defined
First Ionization Energy	24.587 eV
Density	0.0001785 g/cm³
Melting Point	−272.2 °C
Boiling Point	−268.93 °C
Number of Isotopes	2 (Helium-3, Helium-4)
Discoverer	Pierre Janssen, Norman Lockyer
Year	1868
Specific Heat	5.193 J/g·K
Number of Shells	1
Number of Valence Electrons	2