Beryllium (Be) is a strong, lightweight, corrosion-resistant, steel-gray metallic element. It is one of the alkaline earth metals. It is used as an aerospace structural material, as a moderator and reflector in nuclear reactors, in X-ray tube windows, and in a copper alloy used for springs, electrical contacts, and non-sparking tools. The segmented mirror of the James Webb Space Telescope will be made of beryllium.


Beryllium was discovered by N. I. Vauquelin in 1797 but not extracted as a metal until 1828 by Friedrich Wöhler in Berlin and A. A. B. Bussy in Paris. Its name comes from the Greek beryllos for the semi-precious stone beryl, from which beryllium is derived.


Beryllium is relatively unreactive; it forms divalent, tetracoordinate compounds which are very poisonous, and inhalation can lead to an incurable inflammation of the lungs called berylliosis. Beryllium oxide (BeO) is used in ceramics and in electronics.

atomic number 4
relative atomic mass 9.0122
electron configuration 1s22s2
ionization energy first: 899 kJ/mol
second: 1,757 kJ/mol
atomic radius 111 pm
ionic radius 35 pm
melting point 1,287°C (2,349°F)
boiling point 2,500°C (4,532°F)
relative density 1.848