Difference between revisions of "Boron" - New World Encyclopedia

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'''Boron''' (chemical symbol '''B''', [[atomic number]]* 5)
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'''Boron''' (chemical symbol “B,[[atomic number]] “5”) is a [[chemical element]] that is classified as a [[metalloid]]&mdash;its chemical properties are intermediate between those of [[metal]]s and [[nonmetal]]s. It can take the form of a brown, amorphous powder or a hard, black, [[crystal|crystalline]] material. The element is not found free in [[nature]] but occurs abundantly in the ore [[borax]].
  
It is classified as a [[metalloid]]&mdash;some of its properties resemble those of [[metal]]s, and others resemble those of [[nonmetal]]s.
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Elemental boron is used as a dopant in the [[semiconductor]] industry and as a material that produces a green flame in [[pyrotechnic]] flares. Boron filaments are useful for making composites for advanced [[aerospace]] structures, golf clubs, and [[fishing rod]]s. Boric [[acid]] is used in textiles and insecticides, and borates are used in making insulating [[fiberglass]], laundry detergents, antiseptics, adhesives, and a variety of other products. The [[isotope]] boron-10 is used to control reactions in nuclear reactors and as a shield against radiation from [[radioactive]] materials.
. A trivalent element,  
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{{toc}}
Boron is not found free in nature but occurs abundantly in the ore [[borax]]*.
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Boron is an essential plant nutrient, but its physiological role (if any) in humans and animals is poorly understood. The element is nontoxic to humans, and common compounds (such as boric acid and borates) have low toxicity, but some specialized boron [[hydrogen]] compounds are toxic and highly flammable.
 
 
Several [[allotropy|allotropes]] of boron exist; [[amorphous]] boron is a brown powder, though metallic (crystalline) boron is black, hard (9.3 on [[Mohs Scale|Mohs' scale]]), and a weak conductor at room temperature.
 
 
 
Elemental boron is used as a dopant in the semiconductor industry, while boron compounds play important roles as light structural materals, nontoxic insecticides and preservatives, and reagents for chemical synthesis.  
 
 
 
Boron is an essential plant nutrient, and as an ultratrace mineral is necessary for the optimal health of animals, though its physiological role in animals is poorly understood.  
 
  
 
==Occurrence==
 
==Occurrence==
 
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In nature, boron does not appear in elemental form but is found combined in [[borax]], [[boric acid]], [[colemanite]], [[kernite]] (rasorite), [[ulexite]], and [[borate]]s. Boric acid is sometimes found in [[volcano|volcanic]] spring [[water|waters]]. Also, a boron-containing natural [[antibiotic]] named [[boromycin]] has been isolated from ''[[Streptomyces]]''.<ref>R. Hütter, W. Keller-Schien,F. Knüsel, V. Prelog, G.C. Rodgers Jr., P. Suter, G. Vogel, W. Voser, and H. Zähner, "Stoffwechselprodukte von Mikroorganismen. 57. Mitteilung. Boromycin" ''Helvetica Chimica Acta.'' 50(6) (1967): 1533–1539. </ref><ref>J.D. Dunitz, D.M. Hawley, D. Miklos, D.N.J. White, Y. Berlin, R. Marusić, and V. Prelog,  "Structure of boromycin" ''Helvetica Chimica Acta'' 54(6) (1971): 1709–1713.</ref>
In nature, boron does not appear in elemental form but is found combined in [[borax]]*, [[boric acid]]*, [[colemanite]]*, [[kernite]]* (rasorite), [[ulexite]]*, and [[borate]]*s. Boric acid is sometimes found in [[volcano|volcanic]] spring waters. Also, a boron-containing natural [[antibiotic]] named [[boromycin]]* has been isolated from ''[[Streptomyces]]*''.<ref>{{cite journal| author=Hütter | title=| journal=Helv. Chim. Acta. | year= 1967| pages=1533-1539| volume=50}}</ref><ref>{{cite journal| author=Dunitz | title=| journal= Helv. Chim. Acta.| year= 1971| pages=1709-1713| volume=54}}</ref>
 
  
 
[[Image:Borax crystals.jpg|thumb|200px|left|Borax crystals.]]
 
[[Image:Borax crystals.jpg|thumb|200px|left|Borax crystals.]]
  
Economically important sources are from kernite and borax ores, both of which are found in the [[Mojave Desert]]* of [[California]]*, with borax being the main source there. Extensive [[borax]]* deposits are also found in [[Turkey]]. The [[United States]] and [[Turkey]] are the world's largest producers of boron.
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Economically important sources of boron are kernite and borax ores, both of which are found in the [[Mojave Desert]] of [[California]], with borax being the main source there. Extensive [[borax]] deposits are also found in [[Turkey]]. The [[United States]] and Turkey are the world's largest producers of boron.
  
Pure elemental boron is not easy to prepare. The earliest methods involved reduction of [[boric oxide]]* with metals such as [[magnesium]] or [[aluminum]]. The product, however, is almost always contaminated with metal [[boride]]*s. Pure boron can be prepared by reducing volatile boron halogenides with [[hydrogen]] at high temperatures. Highly pure boron, for use in the semiconductor industry, is produced by the high-temperature decomposition of [[diborane]]*, followed by what is called the [[Czochralski process]]*.
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==History and purification==
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Compounds of boron have been known for thousands of years. The name ''boron'' can be traced to the [[Arabic language|Arabic]] ''buraq'', [[Persian language|Persian]] ''burah'', and Turkish ''bor'', which are words for borax. In early [[Egypt]], the process of [[mummification]] depended on an ore known as [[natron]], which contained borates as well as some other common salts. Borax [[glaze]]s were used in [[China]] from 300 C.E., and boron compounds were used in glassmaking in ancient [[Rome]].
  
*Ulexite is a [[borate]]* [[mineral]] that has [[fiber optic]] properties.
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The element was first isolated in 1808 by the English chemist Sir Humphry Davy and independently by French chemists [[Joseph Louis Gay-Lussac]] and [[Louis Jacques Thénard]]. By reducing [[boric acid]] (H<sub>3</sub>BO<sub>3</sub> or B(OH)<sub>3</sub>) with [[sodium]] or [[magnesium]], they obtained boron at about 50 percent purity. It was not until 1824, however, that boron was recognized as a [[chemical element]] by [[Jöns Jakob Berzelius]]. It is generally thought that the first pure boron was produced by American chemist Ezekiel Weintraub in 1909.<ref>Ezekiel Weintraub, "Preparation and properties of pure boron" ''Transactions of the American Electrochemical Society'' 16 (1910): 165–184.</ref>
  
==History==
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Pure, elemental boron is not easy to prepare. When boric acid is melted, it is converted to boron oxide (B<sub>2</sub>O<sub>3</sub>), which can then be reduced with a metal such as magnesium or aluminum. The boron produced, however, is almost always contaminated with the metal [[boride]]. Pure boron can be prepared by reducing volatile boron halogenides with [[hydrogen]] at high temperatures. Highly pure boron, for use in the semiconductor industry, is produced by the high-temperature decomposition of [[diborane]] (B<sub>2</sub>H<sub>6</sub>), followed by what is called the [[Czochralski process]].
 
 
Compounds of boron ([[Arabic language|Arabic]] ''Buraq'', from [[Persian language|Persian]] ''Burah'', from [[Turkish language|Turkish]] ''Bor'') have been known of for thousands of years. In early Egypt, the process of [[mummification]]* depended on an ore known as [[natron]]*, which contained borates as well as some other common salts. Borax [[glaze]]*s were used in [[China]] from CE 300, and boron compounds were used in glassmaking in ancient Rome.
 
 
 
The element was first isolated in 1808 by Sir [[Humphry Davy]], [[Joseph Louis Gay-Lussac]]*, and [[Louis Jacques Thénard]]*. By [[redox|reducing]] [[boric acid]]* with [[sodium]] or [[magnesium]], they obtained boron at about 50 percent purity. These men, however, did not recognize the substance as an element. In 1824, [[Jöns Jakob Berzelius]]* identified boron as an element. It is generally thought that the first pure boron was produced by American chemist W. Weintraub in 1909, but some researchers have cast doubt on the accuracy of that view.<ref>{{cite journal| author= | title=| journal= Z. Angew. Phys.| year=1970| pages=277| volume=29}}</ref>
 
 
 
*Boron was not believed to be useful to the human body until 1989 research suggested its signficance.{{citation needed}}
 
  
 
== Notable characteristics ==
 
== Notable characteristics ==
 
 
In the [[periodic table]], boron is situated at the top of group 13 (former group 3A), just above [[aluminum]], and in period 2, between [[beryllium]] and [[carbon]]. It is classified as a [[metalloid]].
 
In the [[periodic table]], boron is situated at the top of group 13 (former group 3A), just above [[aluminum]], and in period 2, between [[beryllium]] and [[carbon]]. It is classified as a [[metalloid]].
  
Boron exists in different allotropic forms. [[Amorphous]] boron is a brown powder and is produced by certain chemical reactions. It contains boron atoms randomly bonded to one another, without long-range order. By contrast, [[crystalline]] (metallic) boron is black in color and extremely hard (9.3 on [[Mohs Scale|Mohs' scale]]*). It has a high melting point and exists in many [[polymorph]]*s&mdash;forms of boron that differ in their crystal lattice structure.
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Boron exists in different allotropic forms. [[Amorphous]] boron is a brown powder and is produced by certain chemical reactions. It contains boron atoms randomly bonded to one another, without long-range order. By contrast, [[crystalline]] (metallic) boron is black in color and extremely hard (9.3 on [[Mohs Scale|Mohs' scale]]). It has a high melting point and exists in many [[polymorph]]s&mdash;forms of boron that differ in their crystal lattice structure.
  
The best characterized crystalline forms are: two [[rhombohedral]]* forms, α-boron and β-boron, containing 12 and 106.7 atoms in each rhombohedral unit cell, respectively; and a [[tetragonal]]*, 50-atom form. These forms are somewhat analogous to [[diamond]] crystals, but unlike diamond, boron has various possible structures because each boron atom can form three bonds, forcing the atoms to be asymmetrically bonded in three-dimensional space.
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The best characterized crystalline forms are: two [[rhombohedral]] forms, α-boron and β-boron, containing 12 and 106.7 atoms in each rhombohedral unit cell, respectively; and a [[tetragonal]], 50-atom form. These forms are somewhat analogous to [[diamond]] crystals, but unlike diamond, boron has various possible structures because each boron atom can form three bonds, forcing the atoms to be asymmetrically bonded in three-dimensional space.
  
 
Crystalline boron can transmit [[infrared]] light. At standard temperatures, it is a poor conductor of [[electricity]], but it becomes is a good conductor at high temperatures.
 
Crystalline boron can transmit [[infrared]] light. At standard temperatures, it is a poor conductor of [[electricity]], but it becomes is a good conductor at high temperatures.
  
Boron is similar to [[carbon]] in terms of being able to form stable, [[covalent bond|covalently bonded]] molecular networks. On the other hand, each boron atom has one less electron than a carbon atom, and boron behaves as an [[electrophile]]*&mdash;it seeks to form a covalent bond with an element that can provide a pair of electrons to form the bond. The reactions of boron are dominated by this requirement for electrons. Based on this property, boron is called a [[Lewis acid]]*.
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Boron is similar to [[carbon]] in terms of being able to form stable, [[covalent bond|covalently bonded]] molecular networks. On the other hand, each boron atom has one less electron than a carbon atom, and boron behaves as an [[electrophile]]&mdash;it seeks to form a covalent bond with an element that can provide a pair of electrons to form the bond. The reactions of boron are dominated by this requirement for electrons. Based on this property, boron is called a [[Lewis acid]].
  
 
===Isotopes===
 
===Isotopes===
 
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There are 13 known [[isotope]]s of boron. Two stable isotopes occur in nature: <sup>11</sup>B (about 80 percent) and <sup>10</sup>B (about 20 percent). Also, <sup>11</sup>B is a by-product of the [[nuclear power]] industry. The shortest-lived isotope is <sup>7</sup>B which has a [[half-life]] of 3.26500x10<sup>-22</sup> seconds and decays through [[proton|proton emission]] and [[alpha decay]].
There are 13 known isotopes of boron. Two stable [[isotope]]s occur in nature: <sup>11</sup>B (about 80%) and <sup>10</sup>B (about 20%). Also, <sup>11</sup>B is a by-product of the [[nuclear power|nuclear industry]]. The shortest-lived isotope is <sup>7</sup>B which has a [[half-life]]* of 3.26500x10<sup>-22</sup> seconds and decays through [[proton emission]]* and [[alpha decay]]*.
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The <sup>10</sup>B isotope is good at capturing thermal neutrons, such as from [[cosmic ray]]s. It then undergoes [[nuclear fission]], producing a [[gamma ray]], an [[alpha particle]], and a [[lithium]] ion. When this happens within an [[integrated circuit]], the fission products may dump charge into nearby chip structures, resulting in data loss. To avoid this effect in critical [[semiconductor]] designs, "depleted boron" (consisting almost entirely of <sup>11</sup>B) is used.
The <sup>10</sup>B isotope is good at capturing [[thermal neutron]]s, such as from [[cosmic ray]]s. It then undergoes [[nuclear fission]]*, producing a [[gamma ray]], an [[alpha particle]], and a [[lithium]] ion. When this happens within an [[integrated circuit]], the fission products may dump charge into nearby chip structures, resulting in data loss. To avoid this effect in critical [[semiconductor]] designs, "depleted boron" (consisting almost entirely of <sup>11</sup>B) is used.
 
 
 
The ability of <sup>10</sup>B to capture [[thermal neutron]]s has been used in radiation shielding and medical therapy. In nuclear reactors, <sup>10</sup>B is used for reactivity control and in emergency shutdown systems. It can serve either function in the form of [[borosilicate]]* rods or as [[boric acid]]*.
 
 
 
In medical treatment for a tumor, a compound containing <sup>10</sup>B may be attached to the tumor tissue, and the patient is treated with a relatively low dose of thermal neutrons. The <sup>10</sup>B absorbs neutrons and releases short-range alpha radiation. This radiation kills the tumor cells.
 
  
 
== Boron nitride ==
 
== Boron nitride ==
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Boron nitride is a material in which the extra [[electron]] of the [[nitrogen|nitrogen atom]] (compared to a [[carbon]] atom) in some ways compensates for the boron atom's deficiency of an electron (compared to carbon). Boron nitride can be used to make crystals that are extremely hard&mdash;second in hardness only to [[diamond]]. Also, like diamond, boron nitride acts as an electrical [[insulator]], but it is an excellent conductor of heat.
  
Boron nitride is a material in which the extra electron of the nitrogen atom (compared to a carbon atom) in some ways compensates for the boron atom's deficiency of an electron (compared to carbon). Boron nitride can be used to make crystals that are extremely hard, second in hardness only to [[diamond]]. Also, like diamond, boron nitride acts as an electrical [[insulator]]*, but it is an excellent conductor of heat.
+
Like carbon, boron nitride exists in a second form that has structural and [[lubrication|lubricating]] qualities similar to those of [[graphite]]. Like graphite, this form of boron nitride is composed of layers of fused hexagonal sheets. Yet, unlike graphite, these sheets are "in registry." This means that the layers are placed directly above one another, such that a viewer looking down onto the structure would view only the top layer. The polar B-N bonds interfere with electron transfer, so that boron nitride in this form is not an electrical conductor. (By contrast, graphite conducts electricity through a network of pi bonds in the plane of its hexagonal sheets.)
 
 
Like carbon, boron nitride exists in a second form that has structural and [[lubrication|lubricating]]* qualities similar to those of [[graphite]]. Like graphite, this form of boron nitride is composed of layers of fused hexagonal sheets. Yet, unlike graphite, these sheets are "in registry." This means that the layers are placed directly above one another, such that a viewer looking down onto the structure would view only the top layer. The polar B-N bonds interfere with electron transfer, so that boron nitride in this form is not an electrical conductor. (By contrast, graphite conducts electricity through a network of pi bonds in the plane of its hexagonal sheets.)
 
  
 
Boron nitride nanotubes can be constructed in a form analogous to carbon nanotubes.
 
Boron nitride nanotubes can be constructed in a form analogous to carbon nanotubes.
  
 
==Applications==
 
==Applications==
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There are several hundred uses of boron and its compounds. Some of the notable ones are highlighted below.
  
Of the several hundred uses of boron compounds, especially notable uses include:
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* Amorphous boron is used in [[Flare (pyrotechnic)|pyrotechnic flares]], to produce a distinctive green flame.
 
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* In trace amounts, boron is used as a [[dopant]] for P-type [[semiconductor]]s.
* As boron is an essential plant [[micronutrient]], [[borates]]* are used in [[agriculture]].
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* [[Sodium borate]] pentahydrate ([[sodium|Na]]<sub>2</sub>B<sub>4</sub>[[oxygen|O]]<sub>7</sub> • 5H<sub>2</sub>O) is used in large amounts in making insulating [[fiberglass]] and [[sodium perborate]] [[Bleach (chemical)|bleach]].
* Because it produces a distinctive green flame, amorphous boron is used in [[Flare (pyrotechnic)|pyrotechnic flares]]*.
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* [[Sodium borate]] decahydrate ([[sodium|Na]]<sub>2</sub>B<sub>4</sub>[[oxygen|O]]<sub>7</sub> • 10H<sub>2</sub>O, or borax) is used in laundry detergents, antiseptics, adhesives, and anti-corrosion systems, among others.
* [[Boric acid]]* is an important compound used in [[textile]] products. For example, boron compounds are used as nontoxic flame retardants to treat cotton fiber. [http://www.natbat.com/docs/boron.htm]
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* [[Boric acid]] (or orthoboric acid, [[hydrogen|H]]<sub>3</sub>B[[oxygen|O]]<sub>3</sub>)is an important compound used in [[textile]] products. When applied to cotton fibers, it acts as a nontoxic flame retardant. [http://www.natbat.com/docs/boron.htm]
* [[Boric acid]]* is also traditionally used as an [[insecticide]], notably against [[ant]]s and [[cockroach]]es.
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* [[Boric acid]] is also traditionally used as an [[insecticide]], notably against [[ant]]s and [[cockroach]]es.
* Compounds of boron are used extensively in organic synthesis and in the manufacture of [[borosilicate glass|borosilicate]]* and [[borophophosilicate glass|borophosphosilicate]]* [[glass]]es.
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* As boron is an essential plant [[micronutrient]], [[borates]] are used in [[agriculture]].
* Other compounds are used as [[wood]] preservatives, and are particularly attractive in this regard because they have low [[toxicity]]*.
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* Compounds of boron are used extensively in organic chemical syntheses. For example, [[sodium borohydride]] (NaBH<sub>4</sub>) is used for converting [[aldehyde]]s and [[ketone]]s to [[alcohol]]s.
* <sup>10</sup>B is used to control reactions in [[nuclear reactor]]s, as a [[radiation protection|shield]]* against [[Radioactive decay|radiation]]*, and in [[neutron]] detection.
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* Some compounds of boron are used in the manufacture of [[borosilicate glass|borosilicate]] and [[borophophosilicate glass|borophosphosilicate]] [[glass]]es.
* Purified <sup>11</sup>B ([[#Depleted boron|depleted boron]]) is used for [[borosilicate glass]]es in [[radiation hardening|rad-hard]] electronics.
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* Other compounds are used as [[wood]] preservatives, and are particularly attractive in this regard because they have low [[toxicity]].
* Research is being conducted into the production of hydrogen fuel through the interaction of water and a borohydride (such as NaBH<sub>4</sub>). The engine would work by mixing borohydride with water to produce hydrogen as needed, thus solving some present issues of safely transporting hydrogen gas.  The research is being conducted at the University of Minessota, United States by Abu-Hamed and at the Weizmann Institute of Science in Rehovot, Israel. To succeed, the rate of hydrogen production by the small engine needs only to meet the energy demands of the engine. Five kilograms of hydrogen (corresponding to 40 kg of NaBH<sub>4</sub>) has the same amount of energy as twenty gallons (60 kg) of fuel. <ref> (David Adam, Environmental Correspondent, London/ in New Scientist 29/07/06) </ref>
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* Given the ability of <sup>10</sup>B to capture [[thermal neutron]]s, this isotope is used to control reactions in [[nuclear reactor]]s, as a [[radiation protection|shield]] against [[Radioactive decay|radiation]] and in [[neutron]] detection.
* [[Sodium borohydride]] (NaBH<sub>4</sub>), the same chemical as used in the experimental car, is a popular chemical [[Redox|reducing agent]], used (for example) for reducing [[aldehyde]]s and [[ketone]]s to [[alcohol]]s.
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* Purified <sup>11</sup>B ("depleted boron," separated from <sup>10</sup>B) is used for [[borosilicate glass]]es in "rad-hard" (radiation hardened) electronics.
* Boron filaments are high-strength, lightweight materials that are chiefly used for advanced [[aerospace]] structures as a component of [[composite material]]s, as well as limited production consumer and sporting goods such as golf clubs and [[fishing rod]]s.
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* [[Sodium borohydride]] (NaBH<sub>4</sub>) is a popular chemical [[Redox|reducing agent]]. For example, it is used for converting [[aldehyde]]s and [[ketone]]s to alcohols.
* Boron in trace amounts is used as [[dopant]] for [[P-type semiconductor]]s.
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* Boron filaments are high-strength, lightweight materials that are chiefly used in composites for advanced [[aerospace]] structures. They are also used in such items as golf clubs and [[fishing rod]]s.
 
 
Boron compounds are being investigated for use in a broad range of applications, including as components in sugar-permeable membranes, [[carbohydrate]] sensors and [[bioconjugate]]s.
 
 
 
Medicinal applications being investigated include boron [[neutron capture]] therapy and [[medication|drug]] delivery. Other boron compounds show promise in treating [[arthritis]].
 
 
 
[[borane|Hydrides of boron]] are [[oxidation|oxidized]] easily and liberate a considerable amount of [[energy]]. They have therefore been studied for use as possible [[rocket fuel]]s, along with elemental boron.  However, issues of cost, incomplete combustion, and [[boric oxide]] deposits have so far made this use infeasible.
 
 
 
The most economically important compounds of boron are:
 
  
* [[Sodium tetraborate]] pentahydrate ([[sodium|Na]]<sub>2</sub>B<sub>4</sub>[[oxygen|O]]<sub>7</sub> · 5[[water (molecule)|H<sub>2</sub>O]]), which is used in large amounts in making insulating [[fiberglass]] and [[sodium perborate]] [[Bleach (chemical)|bleach]],
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===Potential uses===
* Orthoboric acid ([[hydrogen|H]]<sub>3</sub>B[[oxygen|O]]<sub>3</sub>) or [[boric acid]], used in the production of textile [[fiberglass]] and [[flat panel display]]s or [[eye drop]]s, among many uses, and
 
* [[Sodium tetraborate]] decahydrate ([[sodium|Na]]<sub>2</sub>B<sub>4</sub>[[oxygen|O]]<sub>7</sub> · 10[[water (molecule)|H<sub>2</sub>O]]) or [[borax]], used in the production of adhesives, in anti-corrosion systems and many other uses.
 
  
===Food===
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* Boron compounds are being investigated for use in a broad range of applications, including as components in sugar-permeable membranes, [[carbohydrate]] sensors, and [[bioconjugate]]s.
Boron occurs in all foods produced by plants. Since 1989 its nutritional value has been argued. The U.S. Department of agriculture conducted an experiment in which postmenopausal women took 3 mg of boron a day. The results showed that boron can drop excretion of calcium by 44%, and activate estrogen and vitamin D.
 
  
''See also [[:category:Borate minerals|Borate minerals]].''
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* Some boron compounds show promise in medicine, for drug delivery and treating [[arthritis]].
  
===Analytical quantification===
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* A medical application being investigated is [[neutron capture]] therapy for treating tumors. If a compound containing <sup>10</sup>B is attached to a tumor and the tissue is exposed to a low dose of thermal neutrons, the <sup>10</sup>B absorbs neutrons and releases short-range alpha radiation. This radiation kills the tumor cells.
For determination of boron content in food or materials the [[colorimetry|colorimetric]] curcumin method is used. Boron has to be transferred to [[boric acid]] or [[borate]]s and on reaction with [[curcumin]] in acidic solution a red colored boron-[[chelate]] complex -  [[rosocyanine]] - is formed.
 
  
 +
* [[borane|Hydrides of boron]] are [[oxidation|oxidized]] easily and liberate a considerable amount of [[energy]]. They have therefore been studied for use as possible [[rocket fuel]]s, along with elemental boron. However, issues of cost, incomplete combustion, and [[boric oxide]] deposits have so far made this use infeasible.
  
 +
== Boron in food ==
 +
Boron occurs in all foods produced by plants. Its nutritional value has been argued since at least 1989. The U.S. Department of Agriculture conducted an experiment in which postmenopausal women took three milligrams of boron a day. The results showed that boron can drop excretion of [[calcium]] by 44 percent, and activate [[estrogen]] and vitamin D.
  
 
==Precautions==
 
==Precautions==
Elemental boron is nontoxic and common boron compounds such as borates and boric acid have low toxicity (approximately similar to table salt with the lethal dose being 2 to 3 grams per kg) and therefore do not require special precautions while handling. Some of the more exotic [[borane|boron hydrogen]] compounds, however, ''are'' toxic as well as highly [[flammable]] and do require special handling care.
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Elemental boron is nontoxic and common boron compounds such as borates and boric acid have low toxicity (approximately similar to table salt, with the lethal dose being two to three grams per kilogram) and therefore do not require special precautions while handling. Some of the more exotic [[borane|boron hydrogen]] compounds, however, ''are'' toxic as well as highly [[flammable]] and do require special handling care.
  
==See also==
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== Notes ==
 
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<references />
* [[Chemical element]]
 
* [[Periodic table]]
 
  
 
==References==
 
==References==
<references />
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* Greenwood, N.N., and A. Earnshaw. ''Chemistry of the Elements''. Butterworth-Heinemann, 1997. ISBN 978-0750633659
*[http://periodic.lanl.gov/elements/5.html Los Alamos National Laboratory &ndash; Boron]
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* Muetterties, Earl L. ''The Chemistry of Boron and its Compounds''. John Wiley & Sons, 1967.
 +
* Thomas, Susan E. ''Organic Synthesis: The Roles of Boron and Silicon''. Oxford University Press, 1992. ISBN 978-0198556626
  
 
== External links ==
 
== External links ==
{{Commons|Boron}}
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All links retrieved February 9, 2022.
{{wiktionary|boron}}
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* [http://www.du.edu/~jcalvert/phys/boron.htm Boron]
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* [http://www.inchem.org/documents/ehc/ehc/ehc204.htm Environmental Health Criteria 204: Boron (1998)] by the International Programme on Chemical Safety.
* [http://www.compchemwiki.org/index.php?title=Boron Computational Chemistry Wiki]
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* [http://www.greenfacts.org/boron/boron-1.htm Boron] by GreenFacts.
* [http://www.inchem.org/documents/ehc/ehc/ehc204.htm Environmental Health Criteria 204: Boron (1998)] by the [[International Programme on Chemical Safety|IPCS]].
 
** [http://www.greenfacts.org/boron/boron-1.htm A summary of the above report] by [[GreenFacts]].
 
 
* [http://education.jlab.org/itselemental/ele005.html It's Elemental &ndash; Boron]
 
* [http://education.jlab.org/itselemental/ele005.html It's Elemental &ndash; Boron]
* [http://www.npi.gov.au/database/substance-info/profiles/15.html National Pollutant Inventory - Boron and compounds]
 
 
* [http://www.webelements.com/webelements/elements/text/B/index.html WebElements.com &ndash; Boron]
 
* [http://www.webelements.com/webelements/elements/text/B/index.html WebElements.com &ndash; Boron]
  

Revision as of 14:55, 9 February 2022

5 berylliumboroncarbon
-

B

Al
B-TableImage.png
periodic table
General
Name, Symbol, Number boron, B, 5
Chemical series metalloids
Group, Period, Block 13, 2, p
Appearance black/brown
B,5.jpg
Atomic mass 10.811 (7) g/mol
Electron configuration 1s2 2s2 2p1
Electrons per shell 2, 3
Physical properties
Phase solid
Density (near r.t.) 2.34 g/cm³
Liquid density at m.p. 2.08 g/cm³
Melting point 2349 K
(2076 °C, 3769 °F)
Boiling point 4200 K
(3927 °C, 7101 °F)
Heat of fusion 50.2 kJ/mol
Heat of vaporization 480 kJ/mol
Heat capacity (25 °C) 11.087 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 2348 2562 2822 3141 3545 4072
Atomic properties
Crystal structure rhombohedral
Oxidation states 3
(mildly acidic oxide)
Electronegativity 2.04 (Pauling scale)
Ionization energies
(more)
1st: 800.6 kJ/mol
2nd: 2427.1 kJ/mol
3rd: 3659.7 kJ/mol
Atomic radius 85 pm
Atomic radius (calc.) 87 pm
Covalent radius 82 pm
Miscellaneous
Magnetic ordering nonmagnetic
Electrical resistivity (20 °C) 1.5×104 Ω·m
Thermal conductivity (300 K) 27.4 W/(m·K)
Thermal expansion (25 °C) 5–7 µm/(m·K)
Speed of sound (thin rod) (20 °C) 16200 m/s
Bulk modulus (β form) 185 GPa
Mohs hardness 9.3
Vickers hardness 49000 MPa
CAS registry number 7440-42-8
Notable isotopes
Main article: Isotopes of boron
iso NA half-life DM DE (MeV) DP
10B 19.9%* B is stable with 5 neutrons
11B 80.1%* B is stable with 6 neutrons
*Boron-10 content may be as low as 19.1% and as
high as 20.3% in natural samples. Boron-11 is
the remainder in such cases.

Boron (chemical symbol “B,” atomic number “5”) is a chemical element that is classified as a metalloid—its chemical properties are intermediate between those of metals and nonmetals. It can take the form of a brown, amorphous powder or a hard, black, crystalline material. The element is not found free in nature but occurs abundantly in the ore borax.

Elemental boron is used as a dopant in the semiconductor industry and as a material that produces a green flame in pyrotechnic flares. Boron filaments are useful for making composites for advanced aerospace structures, golf clubs, and fishing rods. Boric acid is used in textiles and insecticides, and borates are used in making insulating fiberglass, laundry detergents, antiseptics, adhesives, and a variety of other products. The isotope boron-10 is used to control reactions in nuclear reactors and as a shield against radiation from radioactive materials.

Boron is an essential plant nutrient, but its physiological role (if any) in humans and animals is poorly understood. The element is nontoxic to humans, and common compounds (such as boric acid and borates) have low toxicity, but some specialized boron hydrogen compounds are toxic and highly flammable.

Occurrence

In nature, boron does not appear in elemental form but is found combined in borax, boric acid, colemanite, kernite (rasorite), ulexite, and borates. Boric acid is sometimes found in volcanic spring waters. Also, a boron-containing natural antibiotic named boromycin has been isolated from Streptomyces.[1][2]

Borax crystals.

Economically important sources of boron are kernite and borax ores, both of which are found in the Mojave Desert of California, with borax being the main source there. Extensive borax deposits are also found in Turkey. The United States and Turkey are the world's largest producers of boron.

History and purification

Compounds of boron have been known for thousands of years. The name boron can be traced to the Arabic buraq, Persian burah, and Turkish bor, which are words for borax. In early Egypt, the process of mummification depended on an ore known as natron, which contained borates as well as some other common salts. Borax glazes were used in China from 300 C.E., and boron compounds were used in glassmaking in ancient Rome.

The element was first isolated in 1808 by the English chemist Sir Humphry Davy and independently by French chemists Joseph Louis Gay-Lussac and Louis Jacques Thénard. By reducing boric acid (H3BO3 or B(OH)3) with sodium or magnesium, they obtained boron at about 50 percent purity. It was not until 1824, however, that boron was recognized as a chemical element by Jöns Jakob Berzelius. It is generally thought that the first pure boron was produced by American chemist Ezekiel Weintraub in 1909.[3]

Pure, elemental boron is not easy to prepare. When boric acid is melted, it is converted to boron oxide (B2O3), which can then be reduced with a metal such as magnesium or aluminum. The boron produced, however, is almost always contaminated with the metal boride. Pure boron can be prepared by reducing volatile boron halogenides with hydrogen at high temperatures. Highly pure boron, for use in the semiconductor industry, is produced by the high-temperature decomposition of diborane (B2H6), followed by what is called the Czochralski process.

Notable characteristics

In the periodic table, boron is situated at the top of group 13 (former group 3A), just above aluminum, and in period 2, between beryllium and carbon. It is classified as a metalloid.

Boron exists in different allotropic forms. Amorphous boron is a brown powder and is produced by certain chemical reactions. It contains boron atoms randomly bonded to one another, without long-range order. By contrast, crystalline (metallic) boron is black in color and extremely hard (9.3 on Mohs' scale). It has a high melting point and exists in many polymorphs—forms of boron that differ in their crystal lattice structure.

The best characterized crystalline forms are: two rhombohedral forms, α-boron and β-boron, containing 12 and 106.7 atoms in each rhombohedral unit cell, respectively; and a tetragonal, 50-atom form. These forms are somewhat analogous to diamond crystals, but unlike diamond, boron has various possible structures because each boron atom can form three bonds, forcing the atoms to be asymmetrically bonded in three-dimensional space.

Crystalline boron can transmit infrared light. At standard temperatures, it is a poor conductor of electricity, but it becomes is a good conductor at high temperatures.

Boron is similar to carbon in terms of being able to form stable, covalently bonded molecular networks. On the other hand, each boron atom has one less electron than a carbon atom, and boron behaves as an electrophile—it seeks to form a covalent bond with an element that can provide a pair of electrons to form the bond. The reactions of boron are dominated by this requirement for electrons. Based on this property, boron is called a Lewis acid.

Isotopes

There are 13 known isotopes of boron. Two stable isotopes occur in nature: 11B (about 80 percent) and 10B (about 20 percent). Also, 11B is a by-product of the nuclear power industry. The shortest-lived isotope is 7B which has a half-life of 3.26500x10-22 seconds and decays through proton emission and alpha decay.

The 10B isotope is good at capturing thermal neutrons, such as from cosmic rays. It then undergoes nuclear fission, producing a gamma ray, an alpha particle, and a lithium ion. When this happens within an integrated circuit, the fission products may dump charge into nearby chip structures, resulting in data loss. To avoid this effect in critical semiconductor designs, "depleted boron" (consisting almost entirely of 11B) is used.

Boron nitride

Boron nitride is a material in which the extra electron of the nitrogen atom (compared to a carbon atom) in some ways compensates for the boron atom's deficiency of an electron (compared to carbon). Boron nitride can be used to make crystals that are extremely hard—second in hardness only to diamond. Also, like diamond, boron nitride acts as an electrical insulator, but it is an excellent conductor of heat.

Like carbon, boron nitride exists in a second form that has structural and lubricating qualities similar to those of graphite. Like graphite, this form of boron nitride is composed of layers of fused hexagonal sheets. Yet, unlike graphite, these sheets are "in registry." This means that the layers are placed directly above one another, such that a viewer looking down onto the structure would view only the top layer. The polar B-N bonds interfere with electron transfer, so that boron nitride in this form is not an electrical conductor. (By contrast, graphite conducts electricity through a network of pi bonds in the plane of its hexagonal sheets.)

Boron nitride nanotubes can be constructed in a form analogous to carbon nanotubes.

Applications

There are several hundred uses of boron and its compounds. Some of the notable ones are highlighted below.

  • Amorphous boron is used in pyrotechnic flares, to produce a distinctive green flame.
  • In trace amounts, boron is used as a dopant for P-type semiconductors.
  • Sodium borate pentahydrate (Na2B4O7 • 5H2O) is used in large amounts in making insulating fiberglass and sodium perborate bleach.
  • Sodium borate decahydrate (Na2B4O7 • 10H2O, or borax) is used in laundry detergents, antiseptics, adhesives, and anti-corrosion systems, among others.
  • Boric acid (or orthoboric acid, H3BO3)is an important compound used in textile products. When applied to cotton fibers, it acts as a nontoxic flame retardant. [1]
  • Boric acid is also traditionally used as an insecticide, notably against ants and cockroaches.
  • As boron is an essential plant micronutrient, borates are used in agriculture.
  • Compounds of boron are used extensively in organic chemical syntheses. For example, sodium borohydride (NaBH4) is used for converting aldehydes and ketones to alcohols.
  • Some compounds of boron are used in the manufacture of borosilicate and borophosphosilicate glasses.
  • Other compounds are used as wood preservatives, and are particularly attractive in this regard because they have low toxicity.
  • Given the ability of 10B to capture thermal neutrons, this isotope is used to control reactions in nuclear reactors, as a shield against radiation and in neutron detection.
  • Purified 11B ("depleted boron," separated from 10B) is used for borosilicate glasses in "rad-hard" (radiation hardened) electronics.
  • Sodium borohydride (NaBH4) is a popular chemical reducing agent. For example, it is used for converting aldehydes and ketones to alcohols.
  • Boron filaments are high-strength, lightweight materials that are chiefly used in composites for advanced aerospace structures. They are also used in such items as golf clubs and fishing rods.

Potential uses

  • Boron compounds are being investigated for use in a broad range of applications, including as components in sugar-permeable membranes, carbohydrate sensors, and bioconjugates.
  • Some boron compounds show promise in medicine, for drug delivery and treating arthritis.
  • A medical application being investigated is neutron capture therapy for treating tumors. If a compound containing 10B is attached to a tumor and the tissue is exposed to a low dose of thermal neutrons, the 10B absorbs neutrons and releases short-range alpha radiation. This radiation kills the tumor cells.
  • Hydrides of boron are oxidized easily and liberate a considerable amount of energy. They have therefore been studied for use as possible rocket fuels, along with elemental boron. However, issues of cost, incomplete combustion, and boric oxide deposits have so far made this use infeasible.

Boron in food

Boron occurs in all foods produced by plants. Its nutritional value has been argued since at least 1989. The U.S. Department of Agriculture conducted an experiment in which postmenopausal women took three milligrams of boron a day. The results showed that boron can drop excretion of calcium by 44 percent, and activate estrogen and vitamin D.

Precautions

Elemental boron is nontoxic and common boron compounds such as borates and boric acid have low toxicity (approximately similar to table salt, with the lethal dose being two to three grams per kilogram) and therefore do not require special precautions while handling. Some of the more exotic boron hydrogen compounds, however, are toxic as well as highly flammable and do require special handling care.

Notes

  1. R. Hütter, W. Keller-Schien,F. Knüsel, V. Prelog, G.C. Rodgers Jr., P. Suter, G. Vogel, W. Voser, and H. Zähner, "Stoffwechselprodukte von Mikroorganismen. 57. Mitteilung. Boromycin" Helvetica Chimica Acta. 50(6) (1967): 1533–1539.
  2. J.D. Dunitz, D.M. Hawley, D. Miklos, D.N.J. White, Y. Berlin, R. Marusić, and V. Prelog, "Structure of boromycin" Helvetica Chimica Acta 54(6) (1971): 1709–1713.
  3. Ezekiel Weintraub, "Preparation and properties of pure boron" Transactions of the American Electrochemical Society 16 (1910): 165–184.

References
ISBN links support NWE through referral fees

  • Greenwood, N.N., and A. Earnshaw. Chemistry of the Elements. Butterworth-Heinemann, 1997. ISBN 978-0750633659
  • Muetterties, Earl L. The Chemistry of Boron and its Compounds. John Wiley & Sons, 1967.
  • Thomas, Susan E. Organic Synthesis: The Roles of Boron and Silicon. Oxford University Press, 1992. ISBN 978-0198556626

External links

All links retrieved February 9, 2022.

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