An Alternative View of Bonding in Boron Trifluoride The chemist, Ron Gillespie, has proposed an alternative bonding model for boron trifluoride, He argues that the bonding is essentially ionic First of all, he notes that as we progress across the Period 2 fluorides from LiF through Bef and BF, to CF it is assumed that there is an abrupt change in bonding from ionic to covalent between beryllium and boron, Second. he contends that the boron - fluorine bond distance is that expected for three close-packed fluoride ions around a boron 3+ on.The greater bond distance in the tetrahedral tetrafluoroborate ion BF, in his view, confirms this hypothesis; four fluoride ions cannot ap- proach the tiny boron ion as closely as three can. In fact, the ratio of B-F bond lengths between BF, and BF, is that predicted by the close packed model. To those who would argue that ionic compounds should not be gases at room temperature, he contends that ionic substances can indeed be gases, provided they are fully coordinated. Thus alu minum fluoride, AlFa, is a solid because six fluorides can surround the aluminum ion, resulting in a three-dimensional (high melting) lattice Boron, by virtue of its small size, can only accommodate the three fluo ride ions. So which is the "correct"model? In chemistry, we often for get that explanations are used to account for observed facts, not vice ersa. Sometimes we use simplistic models that have good predictive alue even when they have limited experimental validity. It would be nice to have the "correct"model but chemistry is rarely as definitive as it is sometimes portrayed in general chemistry courses. Inorganic Fibers In our everyday lives, the fibers we encounter are usually organic, for example, nylon and polyester. These materials are fine for clothing and similar purposes, but most organic fibers have the disadvantages of low melting points, flammability, and low strengths. For materials that are strong and unaffected by high temperatures, inorganic materials fit the specifications best. Some inorganic fibers are well known, for ex ample, asbestos and fiberglass. However, it is the elements boron, car bon, and silicon that currently provide some of the toughest materials for our high-technology world. Carbon fiber is the most widely used-not just for tennis rackets and fishing rods but for aircraft parts as well. The Boeing 767 was the first commercial plane to make sig nificant use of carbon fiber; in fact, about I tonne is incorporated into the structure of cach aircraft. Aircraft constructed with newer technol ogy, such as the Airbus 320, contain a much higher proportion of car bon fibers Fibers of boron and silicon carbide, SiC, are becoming increasingly important in the search for tougher, less fatigue-prone materials. The boron fibers are prepared by reducing boron trichloride with hydrogen gas at about1200°C: 2 BC1(0)+3 H,C-2 B(0)+6 HCI(a) The gaseous boron can then be condensed onto carbon or tungsten microfibers. For example, boron is deposited onto tungsten fibers of 5 um until the diameters of the coated fibers are about 100 um. The typical inorganic fiber prices are several hundred dollars per kilogra so even though production of cach type is mostly in the hundreds of tonnes range, inorganic fiber production is already a billion-dolla220