Helium

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

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[edit]

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