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Atomic weight = 10.811 5B Electron configuration = 1s22s22p1 | |
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Boron is in Group 13 and has a valence electron configuration ns2np1. One of the major sources of boron is the ore borax, Na2[B4O5(OH)4].8H2O. There are large deposits of borax in the Mojave Desert in California. The chemistry of boron is quite different from that of the rest of the Group 13 elements and, in fact, boron has more in common with its diagonal neighbour silicon. At room temperature and 1 atmosphere pressure, elemental boron is a dark brown nonmetallic powder with a structure based on clusters of 12 atoms as shown in the figure to the right. This unit is called an icosahedron because it has 20 faces. Boron fibers are incorporated into plastics to give materials that are stiffer than steel and lighter than aluminum. These materials are used in aircraft, missiles, and body armour. Boron has acidic oxides and forms an extensive range of molecular hydrides many of which have structures based on the icosahedron. One of the most important oxides of boron is boric acid, B(OH)3, a white solid. The acid is used as a fire-retardent, a pesticide, and an antiseptic. Boric acid is an unusual weak acid in that it reacts with water to form the compound that acts as the weak acid: (OH)3B + OH2 ----> (OH)3B-OH2 (OH)3B-OH2 + H2O <----> H3O+ + B(OH)4- The acid has a pKa = 9.14. |
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