Helium

Helium 4.002602(2)   He 2 1s2 [ ? ] Noble gas: Properties: Inert, colorless, odorless, non-toxic, non-flammable gas Uses: Cryogenics, welding, inert purging gas, scientific uses

Helium is a chemical element, having the chemical symbol He and atomic number (number of protons) Z = 2. It has a standard atomic weight of 4.002602 g•mol ⁻¹, and is typically found as a gas in its elemental form.

Helium is a monatomic noble gas. At a pressure of 101.325 kPa, it has a boiling point of -268.93 °C, and a melting point of -272.2 °C. It is of relatively low density--see Benchmark quantities.

Isotopes

The helium atom has two stable isotopes, ³H and ⁴He.