Boron From Wikipedia, the free encyclopedia This article is about the chemical element. For other uses, see Boron (disambiguation). Not to be confused with borium, a tungsten carbide product. Boron 5B - ↑ B ↓ Al beryllium ← boron → carbon Boron in the periodic table Appearance black-brown Boron, shown here in the form of its β-rhombohedral phase (its most thermodynamically stable allotrope)[1] General properties Name, symbol, number boron, B, 5 Pronunciation /ˈbɔərɒn/ Element category metalloid Group, period, block 13, 2, p Standard atomic weight 10.81(1) Electron configuration [He] 2s2 2p1 2, 3 Physical properties Phase solid Liquid density at m.p. 2.08 g·cm−3 Melting point 2349 K, 2076 °C, 3769 °F Boiling point 4200 K, 3927 °C, 7101 °F Heat of fusion 50.2 kJ·mol−1 Heat of vaporization 508 kJ·mol−1 Molar heat capacity 11.087 J·mol−1·K−1 Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 2348 2562 2822 3141 3545 4072 Atomic properties Oxidation states 3, 2, 1[2] (mildly acidic oxide) Electronegativity 2.04 (Pauling scale) Ionization energies (more) 1st: 800.6 kJ·mol−1 2nd: 2427.1 kJ·mol−1 3rd: 3659.7 kJ·mol−1 Atomic radius 90 pm Covalent radius 84±3 pm Van der Waals radius 192 pm Miscellanea Crystal structure rhombohedral Boron has a rhombohedral crystal structure Magnetic ordering diamagnetic[3] Electrical resistivity (20 °C) ~106 Ω·m Thermal conductivity 27.4 W·m−1·K−1 Thermal expansion (25 °C) (β form) 5–7[4] µm·m−1·K−1 Speed of sound (thin rod) (20 °C) 16,200 m·s−1 Mohs hardness ~9.5 CAS registry number 7440-42-8 History Discovery Joseph Louis Gay-Lussac and Louis Jacques Thénard[5] (30 June 1808) First isolation Humphry Davy[6] (9 July 1808) Most stable isotopes Main article: Isotopes of boron iso NA half-life DM DE (MeV) DP 10B 19.9(7)% 10B is stable with 5 neutrons[7] 11B 80.1(7)% 11B is stable with 6 neutrons[7] 10B content may be as low as 19.1% and as high as 20.3% in natural samples. 11B is the remainder in such cases.[8] v t e · references Boron is a chemical element with symbol B and atomic number 5. Because boron is produced entirely by cosmic ray spallation and not by stellar nucleosynthesis,[9] it is a low-abundance element in both the solar system and the Earth's crust. Boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such as borax and kernite. Chemically uncombined boron, which is classed as a metalloid, is found in small amounts in meteoroids, but is not found naturally on Earth. Industrially, very pure boron is produced with difficulty, as boron tends to form refractory materials containing small amounts of carbon or other elements. Several allotropes of boron exist: amorphous boron is a brown powder, and crystalline boron is black, extremely hard (about 9.5 on the Mohs scale), and a poor conductor at room temperature. Elemental boron is used as a dopant in the semiconductor industry. The major industrial-scale uses of boron compounds are in sodium perborate bleaches, and (Owens-Corning) Borosilicate glass which it trademarked as Pyrex, with greater strength and breakage resistance (thermal shock resistance) than ordinary soda lime glass. Boron polymers and ceramics play specialized roles as high-strength lightweight structural and refractory materials. Boron compounds are used in silica-based glasses and ceramics to give them resistance to thermal shock. Boron-containing reagents are used as intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are used, or are in study. Natural boron is composed of two stable isotopes, one of which (boron-10) has a number of uses as a neutron-capturing agent. In biology, borates have low toxicity in mammals (similar to table salt), but are more toxic to arthropods and are used as insecticides. Boric acid is mildly antimicrobial, and a natural boron-containing organic antibiotic is known.[10] Boron is essential to life. Small amounts of boron compounds play a strengthening role in the cell walls of all plants, making boron necessary in soils. Experiments indicate a role for boron as an ultratrace element in animals, but its role in animal physiology is unknown. Contents [hide] 1 History 2 Characteristics 2.1 Allotropes 2.2 Chemistry of the element 2.2.1 Chemical compounds 2.2.1.1 Organoboron chemistry 2.2.1.2 Compounds of B(I) and B(II) 2.3 Isotopes 2.3.1 Commercial isotope enrichment 2.3.2 Enriched boron (boron-10) 2.3.3 Depleted boron (boron-11) 2.3.4 NMR spectroscopy 2.4 Occurrence 3 Production 3.1 Market trend 4 Applications 4.1 Glass and ceramics 4.2 Detergent formulations and bleaching agents 4.3 Insecticides 4.4 Semiconductors 4.5 Magnets 4.6 High-hardness and abrasive compounds 4.6.1 Boron carbide 4.6.2 Other superhard boron compounds 4.7 Shielding in nuclear reactors 4.8 Other nonmedical uses 4.9 Pharmaceutical and biological applications 4.10 Research areas 5 Natural biological role 5.1 Analytical quantification 5.2 Health issues and toxicity 6 See also 7 References 8 External links History[edit] The word boron was coined from borax, the mineral from which it was isolated, by analogy with carbon, which it resembles chemically. For the etymology of borax, see that article. Sassolite Borax glazes were used in China from AD 300, and some tincal (crude borax) reached the West, where the Persian alchemist Jābir ibn Hayyān seems to mention it in AD 700. Marco Polo brought some glazes back to Italy in the 13th century. Agricola, around 1600, reports the use of borax as a flux in metallurgy. In 1777, boric acid was recognized in the hot springs (soffioni) near Florence, Italy, and became known as sal sedativum, with mainly medical uses. The rare mineral is called sassolite, which is found at Sasso, Italy. Sasso was the main source of European borax from 1827 to 1872, at which date American sources replaced it.[11][12] Boron compounds were relatively rarely used chemicals until the late 1800s when Francis Marion Smith's Pacific Coast Borax Company first popularized these compounds and made them in volume and hence cheap.[13] Boron was not recognized as an element until it was isolated by Sir Humphry Davy[6] and by Joseph Louis Gay-Lussac and Louis Jacques Thénard.[5] In 1808 Davy observed that electric current sent through a solution of borates produced a brown precipitate on one of the electrodes. In his subsequent experiments he used potassium to reduce boric acid instead of electrolysis. He produced enough boron to confirm a new element and named the element boracium.[6] Gay-Lussac and Thénard used iron to reduce boric acid at high temperatures. They showed by oxidizing boron with air that boric acid is an oxidation product of boron.[5][14] Jöns Jakob Berzelius identified boron as an element in 1824.[15] Pure boron was arguably first produced by the Ameri