boron
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What is boron?
Boron (B) is a chemical element and semimetal in Group 13 (IIIa) of the periodic table. Boron is essential for plant growth and has wide industrial applications.
Key properties of boron:
* Atomic number: 5
* Oxidation state: +3
* It is a black, lustrous semiconductor that conducts electricity like a metal at high temperatures and acts as an insulator at low temperatures.
* It is hard enough to scratch some abrasives, but too brittle for use in tools.
* It occurs as borax, kernite, and tincalconite, which are hydrated sodium borates.Boron is used to increase hardness in steel and as a doping agent to silicon and germanium to modify electrical conductivity. Boron-10 is also used in neutron shields and in boron neutron capture therapy for treating brain tumors. Boron combines with oxygen to form borate minerals, some of which are borax, colemanite, inyoite, kernite and tincalconite.
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Where is boron found in nature?
Boron, constituting about 0.001 percent of Earth's crust, is never found in its pure form in nature. It mainly occurs in combined forms, such as borax, kernite, and tincalconite, which are hydrated sodium borates. These are the major commercial sources of boron, especially concentrated in the arid regions of California. Boron is also found in widely dispersed minerals like colemanite, ulexite, and tourmaline. Additionally, sassolite, which is natural boric acid, is notably found in Italy. Seawater also contains boron.
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What are some common uses of boron?
Boron is a versatile element with a variety of uses across industries.
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Agriculture Boron is essential in trace amounts for plant growth, preventing disorders like stunted growth and beet dry rot. Borates can be applied to soil to counter boron deficiency, but in excess, they act as herbicides.
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Alloys and metallurgy Boron increases steel hardness and acts as a deoxidizer in nonferrous metals. It's also used as a degasifier in copper alloys and to refine grain in aluminum castings.
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Nuclear applications The boron-10 isotope is a strong neutron absorber, making it useful in neutron shields and in boron neutron capture therapy (BNCT) for treating tumors.
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Industrial applications Borax is a component in glass and pottery glazes, a solvent in metallurgy, and a flux in welding and soldering. Boron carbide is an extremely hard material used as an abrasive and in composite materials. Boron nitride, similar to carbon, has a very hard allotropic form useful as a high-temperature abrasive.
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Other uses Boric acid is used as a mild antiseptic, fire retardant, and in electroplating solutions.
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What are some properties of boron as an element?
Boron (B) is a chemical element and semimetal in Group 13 (IIIa) of the periodic table. It is essential for plant growth and has wide industrial applications.
Boron's properties include:
- Atomic number: 5
- Atomic weight: [10.806, 10.821]
- Melting point: 2,200 °C (4,000 °F)
- Boiling point: 2,550 °C (4,620 °F)
- Specific gravity: 2.34 (at 20 °C [68 °F])
- Oxidation state: +3
- Electron configuration: 1sÂČ2sÂČ2pÂč
In its compounds, boron has an oxidation state of +3 and is covalently bonded. Pure crystalline boron is a lustrous, black semiconductor. It is hard enough to scratch some abrasives but too brittle for tools. Boron combines with oxygen to form borates. The most familiar borate is sodium tetraborate, commonly known as borax (NaâBâOââą10HâO).
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How does boron combine with other elements to form compounds?
Boron, a semimetal element, exhibits a +3 oxidation state when forming compounds. Boron's first three ionization energies are too high to form compounds containing the B3+ ion, so it bonds covalently.
Boron can be three- or four-coordinated, forming compounds with other elements. Three-coordinated boron derivatives are planar molecules that readily form donor-acceptor complexes with compounds containing lone pairs of electrons. In these adducts, the boron atom is four-coordinated, with the four groups being tetrahedrally arranged around it.
Boron also forms boranes with hydrogen, boron carbides with carbon, borides with metals, and boron nitride with nitrogen. Boron reacts with all halogen elements to give monomeric, highly reactive trihalides.
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Why is boron important in plant growth and industry?
Boron is vital for plant growth and has diverse industrial applications. In plants, boron is essential for the normal growth and function of apical meristems, which are the growing tips of plant shoots. Boron deficiency can cause stunted, misshapen growth, and other disorders, which can be alleviated by applying soluble borates to the soil.
Industrially, boron is used to increase hardness in steel and as a deoxidizer in the nonferrous-metals industry. Boron compounds like borax are used in glass and pottery glazes, metallurgy, welding, soldering, fertilizer, soap, disinfectants, mouthwash, and water softeners. Boric acid is used as a mild antiseptic, fire retardant, and in electroplating solutions. Boron carbide is an extremely hard abrasive. Boron nitride can be used as a high-temperature abrasive.
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News •
boron (B), chemical element, semimetal of main Group 13 (IIIa, or boron group) of the periodic table, essential to plant growth and of wide industrial application.
| atomic number | 5 |
|---|---|
| atomic weight | [10.806, 10.821] |
| melting point | 2,200 °C (4,000 °F) |
| boiling point | 2,550 °C (4,620 °F) |
| specific gravity | 2.34 (at 20 °C [68 °F]) |
| oxidation state | +3 |
| electron configuration | 1s22s22p1 |
Properties, occurrence, and uses
Pure crystalline boron is a black, lustrous semiconductor; i.e., it conducts electricity like a metal at high temperatures and is almost an insulator at low temperatures. It is hard enough (9.3 on Mohs scale) to scratch some abrasives, such as carborundum, but too brittle for use in tools. It constitutes about 0.001 percent by weight of Earthâs crust. Boron occurs combined as borax, kernite, and tincalconite (hydrated sodium borates), the major commercial boron minerals, especially concentrated in the arid regions of California, and as widely dispersed minerals such as colemanite, ulexite, and tourmaline. Sassoliteânatural boric acidâoccurs especially in Italy.
Boron was first isolated (1808) by French chemists Joseph-Louis Gay-Lussac and Louis-Jacques Thenard and independently by British chemist Sir Humphry Davy by heating boron oxide (B2O3) with potassium metal. The impure amorphous product, a brownish black powder, was the only form of boron known for more than a century. Pure crystalline boron may be prepared with difficulty by reduction of its bromide or chloride (BBr3, BCl3) with hydrogen on an electrically heated tantalum filament.
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Limited quantities of elemental boron are widely used to increase hardness in steel. Added as the iron alloy ferroboron, it is present in many steels, usually in the range 0.001 to 0.005 percent. Boron is also used in the nonferrous-metals industry, generally as a deoxidizer, in copper-base alloys and high-conductance copper as a degasifier, and in aluminum castings to refine the grain. In the semiconductor industry, small, carefully controlled amounts of boron are added as a doping agent to silicon and germanium to modify electrical conductivity.
In the form of boric acid or borates, traces of boron are necessary for growth of many land plants and thus are indirectly essential for animal life. Typical effects of long-term boron deficiency are stunted, misshapen growth; vegetable âbrown heartâ and sugar beet âdry rotâ are among the disorders due to boron deficiency. Boron deficiency can be alleviated by the application of soluble borates to the soil. In excess quantities, however, borates act as unselective herbicides. Gigantism of several species of plants growing in soil naturally abundant in boron has been reported. It is not yet clear what the precise role of boron in plant life is, but most researchers agree that the element is in some way essential for the normal growth and functioning of apical meristems, the growing tips of plant shoots.
Pure boron exists in at least four crystalline modifications or allotropes. Closed cages containing 12 boron atoms arranged in the form of an icosahedron occur in the various crystalline forms of elemental boron.
Crystalline boron is almost inert chemically at ordinary temperatures. Boiling hydrochloric acid does not affect it, and hot concentrated nitric acid only slowly converts finely powdered boron to boric acid (H3BO3). Boron in its chemical behaviour is nonmetallic.
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In nature, boron consists of a mixture of two stable isotopesâboron-10 (19.9 percent) and boron-11 (80.1 percent); slight variations in this proportion produce a range of ±0.003 in the atomic weight. Both nuclei possess nuclear spin (rotation of the atomic nuclei); that of boron-10 has a value of 3 and that of boron-11, 3/2, the values being dictated by quantum factors. These isotopes are therefore of use in nuclear magnetic resonance spectroscopy, and spectrometers specially adapted to detecting the boron-11 nucleus are available commercially. The boron-10 and boron-11 nuclei also cause splitting in the resonances (that is, the appearance of new bands in the resonance spectra) of other nuclei (e.g., those of hydrogen atoms bonded to boron).
The boron-10 isotope is unique in that it possesses an extremely large capture cross section (3,836 barns) for thermal neutrons (i.e., it readily absorbs neutrons of low energy). The capture of a neutron by a nucleus of this isotope results in the expulsion of an alpha particle (nucleus of a helium atom, symbolized α):
Since the high-energy alpha particle does not travel far in normal matter, boron and some of its compounds have been used in the fabrication of neutron shields (materials not penetrable by neutrons). In the Geiger counter, alpha particles trigger a response, whereas neutrons do not; hence, if the gas chamber of a Geiger counter is filled with a gaseous boron derivative (e.g., boron trifluoride), the counter will record each alpha particle produced when a neutron that passes into the chamber is captured by a boron-10 nucleus. In this way, the Geiger counter is converted into a device for detecting neutrons, which normally do not affect it.
The affinity of boron-10 for neutrons also forms the basis of a technique known as boron neutron capture therapy (BNCT) for treating patients suffering from brain tumours. For a short time after certain boron compounds are injected into a patient with a brain tumour, the compounds collect preferentially in the tumour; irradiation of the tumour area with thermal neutrons, which cause relatively little general injury to tissue, results in the release of a tissue-damaging alpha particle in the tumour each time a boron-10 nucleus captures a neutron. In this way destruction can be limited preferentially to the tumour, leaving the normal brain tissue less affected. BNCT has also been studied as a treatment for tumours of the head and neck, the liver, the prostate, the bladder, and the breast.