The only nonmetal of group 13 of the periodic table, boron is electron deficient with vacant p-orbitals and forms complex covalent bonds.
Boron combines with other elements to form a variety of compounds. Many of these are amphoteric, dissolving in either acid or base.
The simplest elemental boron allotrope is a-rhombohedral (a-R), containing regular B12 icosahedra in a cubic close-packed lattice. Crystalline boron also exists in g-orthorhombic (g) and b-tetragonal (b-T) structures, with each of these being stable at room temperature.
In addition to its crystalline forms, elemental boron can exist in an amorphous state, which contains a random array of boron icosahedra that are bonded randomly without long-range order. This amorphous phase is inert chemically at ordinary temperatures, but it can be slowly oxidized by a mixture of hot concentrated nitric acid and sodium dichromate or by hydrogen peroxide.
The most common naturally occurring boron compounds are boric acid and sodium borate, which occur as a mineral in the earth’s crust. Other important boron-containing compounds are boron nitride (BN) and boron trihalides (BX3), which are formed when boron is heated with excess nitrogen or halogen. These compounds are used to make a wide range of applications including borosilicate glass, enamels for covering steel, and NdFeB magnets. These high-strength permanent magnetics are used in electric motors, wind turbines, and other electronic devices. They are also used in shielding nuclear reactors to prevent radionuclide release. These boron-containing materials are also used to create abrasives and other hard and wearable materials.