Boron
. Boron, symbol B, hard, brittle semimetallic element with an atomic number of 5. Boron is in group 13 (or IIIa) of the periodic table . Compounds of boron, notably borax, have been known since early times, but the pure element was first prepared in 1808 by the French chemists Joseph Gay-Lussac and Baron Louis Thénard, and independently by the British chemist Sir Humphry Davy . It is a trace element needed for plant growth, but toxic in excess. Research suggests that it is also nutritionally important for bone health in humans and other vertebrates. Pure boron, as usually prepared, is an amorphous powder. A crystalline form can be prepared, however, by dissolving boron in molten aluminum and cooling slowly. The atomic weight of boron is 10.81; the element melts at about 2180°C (about 3956°F), boils at about 3650°C (about 6602°F), and has a specific gravity of 2.35. Boron does not react with water or hydrochloric acid and is unaffected by air at ordinary temperatures. At red heat it co