boron

boron
Name	boron
Category	metalloid
Group	13
Standard atomic weight	10.81
Electron configuration	[He] 2s² 2p¹
Phase	solid
Melting point	2349 K
Boiling point	4200 K
Density	2.34 g/cm³
Appearance	black-brown

boron. It is a low-abundance element in the Solar System and Earth's crust, typically found combined in compounds like borax. Classified as a metalloid, it exhibits properties intermediate between those of carbon and aluminum. The element is essential in numerous industrial and technological applications, from glass manufacturing to semiconductor doping, and also plays a significant, if nuanced, role in biology.

Properties

Boron in its crystalline form is a brittle, dark substance with exceptional hardness, ranking just below diamond and cubic boron nitride on the Mohs scale. It is a poor conductor of electricity at room temperature but becomes a good conductor at high temperatures, a characteristic of a semiconductor. The element has two stable isotopes, boron-10 and boron-11, with the former having a high neutron cross-section, making it crucial for applications in nuclear reactors. Its chemical bonding is notably complex, often involving multicenter bonds, as seen in the structure of boranes.

History

Borax, a compound containing the element, was known to ancient civilizations; it was used in Mesopotamia for gold refining and later by the Egyptians in mummification. The substance was traded along the Silk Road under names like "tincal." In 1808, the element was first isolated independently by Sir Humphry Davy in London and by Joseph Louis Gay-Lussac and Louis Jacques Thénard in Paris through electrolysis of boric acid. The pure, crystalline form was not produced until the 20th century, with pioneering work by the American chemist Ezekiel Weintraub.

Occurrence and production

Economically viable sources are geographically concentrated, with the largest deposits found in the Mojave Desert in the United States and in regions of Turkey near the Sea of Marmara. The primary source is the mineral kernite, which is processed into borax and colemanite. Industrial production typically involves the high-temperature reduction of boron trioxide with magnesium, a method known as the Mond process. Major producers include the Rio Tinto Group through its U.S. Borax operations and the Turkish state-owned company Eti Maden.

Compounds

The most common oxide is boron trioxide, a component of borosilicate glass used in laboratory ware like Pyrex. Important hydrides include diborane and the larger family of boranes, studied extensively by Alfred Stock and later by William Lipscomb, who won the Nobel Prize in Chemistry for his work on their structure. In organic chemistry, boronic acids are vital intermediates in the Suzuki reaction, a pivotal method for forming carbon-carbon bonds developed by Akira Suzuki. Another significant compound is boron nitride, which exists in forms analogous to graphite and diamond.

Applications

A primary use is in fiberglass and insulation materials, with borosilicate glass being valued for its thermal shock resistance in products from laboratory equipment to cookware. In metallurgy, it is added to steel as a microalloying element to improve hardenability. The isotope boron-10 is critical in nuclear applications, serving as a neutron absorber in control rods for reactors like those operated by the Tennessee Valley Authority and as a component in radiation shielding. It is also a essential dopant in the semiconductor industry, used to create p-type semiconductors in devices manufactured by companies such as Intel and TSMC.

Biological role

It is an essential micronutrient for plants, influencing cell wall structure and strength, with deficiency causing issues in crops like apple trees in Washington. In animals and humans, it is involved in bone metabolism and the function of enzymes such as those related to hormone action, though its precise biochemical mechanisms are still under investigation. Some boron compounds, like bortezomib, are used as chemotherapy agents, targeting the proteasome in cancers such as multiple myeloma. Research into its role in arthritis and osteoporosis continues at institutions like the USDA and various university medical centers.

Category:Chemical elements Category:Metalloids