Boron

Boron has three valence electrons ([He]2s2 2p1), but they are held too tightly to be given away, so boron never forms a simple B3+ ion. Instead it bonds covalently, and in many compounds it ends up with only six electrons around it instead of eight. That electron deficiency makes molecules like boron trifluoride strong Lewis acids that grab lone pairs from other molecules, and it drives boron hydrides such as diborane to form unusual three-centre, two-electron bonds. Elemental boron is a hard, black, semiconducting metalloid built from clusters of 12 atoms.

Boron is rare in the universe because stars do not make much of it; most was formed by cosmic rays splitting heavier nuclei in space. On Earth, however, it is concentrated in evaporite deposits of borate minerals, notably in Turkey and California. Adding boron oxide to glass lowers its thermal expansion, giving borosilicate glass that survives sudden temperature changes. Boron is also a key ingredient of neodymium-iron-boron magnets, and the isotope boron-10 absorbs neutrons strongly, so it is used in reactor control rods and shielding.

Discovery

In 1808 Joseph Louis Gay-Lussac and Louis Jacques Thénard in Paris, and Humphry Davy in London, independently obtained impure boron by heating boric acid with potassium. Jöns Jacob Berzelius confirmed it as an element in 1824, but truly pure boron was not made until Ezekiel Weintraub succeeded in 1909. The name combines borax, from the Persian burah, with the ending of carbon, which boron resembles in some ways.