View source for Boron

{{otheruses}}
{{Elementbox
|name=boron
|number=5
|symbol=B
|left=[[beryllium]]
|right=[[carbon]]
|above=-
|below=[[aluminium|Al]]
|series=metalloid
|series comment=
|group=13
|period=2
|block=p
|series color=
|phase color=
|appearance=black/brown
|image name=B,5
|image size=
|image name comment=
|image name 2=
|image name 2 comment=
|atomic mass=10.811
|atomic mass 2=7
|atomic mass comment=
|electron configuration=1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>1</sup>
|electrons per shell=2, 3
|color=
|phase=solid
|phase comment=
|density gplstp=
|density gpcm3nrt=2.34
|density gpcm3mp=2.08
|melting point K=2349
|melting point C=2076
|melting point F=3769
|boiling point K=4200
|boiling point C=3927
|boiling point F=7101
|triple point K=
|triple point kPa=
|critical point K=
|critical point MPa=
|heat fusion=50.2
|heat vaporization=480
|heat capacity=11.087
|vapor pressure 1=2348
|vapor pressure 10=2562
|vapor pressure 100=2822
|vapor pressure 1 k=3141
|vapor pressure 10 k=3545
|vapor pressure 100 k=4072
|vapor pressure comment=
|crystal structure=rhombohedral
|oxidation states=4,<ref>{{cite web|url=http://bernath.uwaterloo.ca/media/78.pdf|title=Fourier Transform Spectroscopy: B<sup>4</sup>&Sigma;<sup>−</sup>−X<sup>4</sup>&Sigma;<sup>−</sup>|author=W.T.M.L. Fernando, L.C. O'Brien, P.F. Bernath|publisher=University of Arizona, Tucson|accessdate=2007-12-10}}</ref> 3, 1<ref>{{cite web|url=http://bernath.uwaterloo.ca/media/125.pdf|title=Infrared Emission Spectroscopy of BF and AIF|author=K.Q. Zhang, B.Guo, V. Braun, M. Dulick, P.F. Bernath|accessdate=2007-12-10|University of Waterloo, Waterloo, Ontario}}</ref>
|oxidation states comment=mildly [[acid]]ic oxide
|electronegativity=2.04
|number of ionization energies=4
|1st ionization energy=800.6
|2nd ionization energy=2427.1
|3rd ionization energy=3659.7
|atomic radius=[[1 E-11 m|85]]
|atomic radius calculated=[[1 E-11 m|87]]
|covalent radius=[[1 E-11 m|82]]
|Van der Waals radius=
|magnetic ordering=nonmagnetic
|electrical resistivity=
|electrical resistivity at 0=
|electrical resistivity at 20=1.5×10<sup>4</sup>
|thermal conductivity=27.4
|thermal conductivity 2=
|thermal diffusivity=
|thermal expansion=
|thermal expansion at 25=5&ndash;7
|speed of sound=
|speed of sound rod at 20=16200
|speed of sound rod at r.t.=
|Young's modulus=
|Shear modulus=
|Bulk modulus=(β form) 185
|Poisson ratio=
|Mohs hardness=9.3
|Vickers hardness=49000
|Brinell hardness=
|CAS number=7440-42-8
|isotopes=
{{Elementbox_isotopes_stable | mn=10 | sym=B | na=18.8%* | n=5 }}
{{Elementbox_isotopes_stable | mn=11 | sym=B | na=81.2%* | n=6 }}
|isotopes comment=*<small>Boron-10 content may be as low as 19.1% and as<br />high as 20.3% in natural samples. Boron-11 is<br />the remainder in such cases.</small>
}}
'''Boron''' ({{pronEng|ˈbɔərɒn}}) is a [[chemical element]] with [[atomic number]] 5 and the chemical symbol '''B'''. Boron is a trivalent [[nonmetal]]lic element which  occurs abundantly in the [[evaporite]] [[ore]]s [[borax]] and [[ulexite]]. Boron is never found as a free element in nature. 

Several [[allotropy|allotropes]] of boron  exist; [[amorphous]] boron is a brown powder, though 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 materials, nontoxic insecticides and preservatives, and reagents for chemical synthesis. 

Boron is an essential plant [[nutrient]], although soil concentrations of > 1.0 ppm can cause marginal and tip necrosis in leaves as well as poor overall growth performance.  Levels as low as 0.8 ppm can cause these same symptoms to appear in plants particularly sensitive to boron in the soil.  Nearly all plants, even those somewhat tolerant of boron in the soil, will show at least some symptoms of boron toxicity when boron in the soil is greater than 1.8 ppm.  When boron in the soil exceeds 2.0 ppm, few plants will perform well.  Plants  sensitive to boron in the soil may not survive.  When boron levels in plant tissue exceed 200 ppm symptoms of boron toxicity are likely to appear.  As an [[ultratrace element]], boron is necessary for the optimal health of animals, though its physiological role in animals is poorly understood.  

== Characteristics ==
Brown amorphous boron is a product of certain chemical reactions. It contains boron atoms randomly bonded to each other without long range order.

[[Crystalline]] boron, a very hard black material with a high melting point, exists in many [[polymorphism (materials science)|polymorphs]].  Two [[rhombohedral]] forms, α-boron and β-boron containing 12 and 106.7 atoms in the rhombohedral unit cell respectively, and 50-atom [[tetragonal]] boron are the three most characterised crystalline forms.

Optical characteristics of crystalline/elemental boron include the transmittance of [[infrared]] light. At standard temperatures, elemental boron is a poor [[electrical conductivity|electrical conductor]], but is a good electrical conductor at high temperatures.

Chemically boron is [[electron]]-deficient, possessing a vacant [[p-block|p-orbital]]. It is an [[electrophile]]. Compounds of boron often behave as [[Lewis acid]]s, readily bonding with electron-rich substances to compensate for boron's electron deficiency. The reactions of boron are dominated by such requirement for electrons.  Also, boron is the least [[electronegativity|electronegative]] non-metal, meaning that it is usually [[oxidized]] (loses electrons) in reactions.

Boron is also similar to [[carbon]] with its capability to form stable [[covalent bond|covalently bonded]] molecular networks. Boron is also used for heat resistant alloys. Boron forms a polyatomic  B(II), such as B<sub>2</sub>F<sub>4</sub>.<ref>{{cite web|url=http://lb.chemie.uni-hamburg.de/search/index.php?content=166/dGp23678|title=Compound Descriptions: B<sub>2</sub>F<sub>4</sub>|accessdate=2007-12-10|publisher=Landol Börnstein Substance/Property Index}}</ref>

== Applications ==
* In automobiles: it is proposed that by reacting water with elemental boron, hydrogen could be produced to be burnt in an internal combustion engine or fed to a fuel cell to generate electricity.<ref>http://www.newscientisttech.com/channel/tech/mg19125621.200</ref>

=== <sup>10</sup>B and <sup>11</sup>B NMR spectroscopy ===
Both <sup>10</sup>B (18.8 percent) and <sup>11</sup>B (81.2 percent) possess [[nuclear spin]]; that of boron-10 has a value of 3 and that of boron-11, 3/2. 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]] of attached nuclei.

==== B-10 depleted boron ====   
The <sup>10</sup>B isotope is good at capturing [[thermal neutron]]s from [[cosmic radiation]].  It then undergoes [[Nuclear fission|fission]] - producing a [[gamma ray]], an [[alpha particle]], and a [[lithium]] ion. When this happens inside of an [[integrated circuit]], the fission products may then dump charge into nearby chip structures, causing data loss (bit flipping, or [[single event upset]]). In critical [[semiconductor]] designs, '''depleted boron'''—consisting almost entirely of <sup>11</sup>B—is used to avoid this effect, as one of [[radiation hardening]] measures. <sup>11</sup>B is a by-product of the [[nuclear power|nuclear industry]]. <sup>11</sup>boron is also a candidate as a fuel for [[aneutronic fusion]].

==== B-10 enriched boron ====
The <sup>10</sup>B isotope is good at capturing [[thermal neutron]]s, and this quality has been used in both radiation shielding and in [[boron neutron capture therapy]] where a tumor is treated with a compound containing <sup>10</sup>B is attached to a muscle, and the patient treated with a relatively low dose of thermal neutrons which go on to cause energetic and short range alpha radiation in the tissue treated with the boron isotope. 

[[Image:Neutroncrosssectionboron.png|left|200px|thumb|Neutron cross section of boron (Black is <sup>10</sup>B and blue is <sup>11</sup>B)]]
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 [[pressurized water reactor]]s, boric acid is added to the reactor coolant when the plant is shut down for refueling. It is then slowly filtered out over many months as fissile material is used up and the fuel becomes less reactive.

In future manned interplanetary spacecraft, <sup>10</sup>B has a theoretical role as structural material (as boron fibers or BN nanotube material) which also would serve a special role in the radiation shield. One of the difficulties in dealing with [[cosmic rays]] which are mostly high energy protons, is that some secondary radiation from interaction of cosmic rays and spacecraft structural materials, is in the form of high energy [[spallation]] neutrons. Such neutrons can be moderated by materials high in light elements such as structural polyethylene, but the moderated neutrons continue to be a radiation hazard unless actively absorbed in a way which dumps the absorption energy in the shielding, far away from biological systems. Among light elements that absorb thermal neutrons, <sup>6</sup>Li and <sup>10</sup>B appear as potential spacecraft structural materials able to do double duty in this regard.

=== Market trend ===
Estimated global consumption of boron rose to a record 1.8 million tonnes of B<sub>2</sub>O<sub>3</sub> in 2005 following a period of strong growth in demand from Asia, Europe and North America. Boron mining and refining capacities are considered to be adequate to meet expected levels of growth through the next decade.
The form in which boron is consumed has changed in recent years. The use of beneficiated ores like [[colemanite]] has declined following concerns over [[arsenic]] content. Consumers have moved towards the use of refined borates or boric acid that have a lower pollutant content. 

Increasing demand for boric acid has led a number of producers to invest in additional capacity. Eti Mine opened a new 100,000 tonnes per year capacity boric acid plant at Emet in 2003. [[Rio Tinto]] increased the capacity of its Boron plant from 260,000 tonnes per year in 2003 to 310,000 tonnes per year by May 2005, with plans to grow this to 366,000 tonnes per year in 2006.

Chinese boron producers have been unable to meet rapidly growing demand for high quality borates. This has led to imports of disodium tetraborate growing by a hundredfold between 2000 and 2005 and boric acid imports increasing by 28% per year over the same period. 

The rise in global demand has been driven by high rates of growth in [[fiberglass]] and borosilicate production. A rapid increase in the manufacture of reinforcement-grade fiberglass in Asia with a consequent increase in demand for borates has offset the development of boron-free reinforcement-grade fiberglass in Europe and the USA. The recent rises in energy prices can be expected to lead to greater use of insulation-grade fiberglass, with consequent growth in the use of boron. 

Roskill Consulting Group forecasts that world demand for boron will grow by 3.4% per year to reach 21 million tonnes by 2010. The highest growth in demand is expected to be in Asia where demand could rise by an average 5.7% per year.<ref>http://www.roskill.com/reports/prePublication/prepubboron</ref>

== Boron compounds ==
{{Seealso|Category:Boron compounds}}

=== The most economically important compounds of boron ===

* [[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]],
* 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.
* [[Boron nitride]] is a material in which the extra electron of nitrogen (with respect to carbon) in some ways compensates for boron's deficiency of an electron.
*Boron reacts with [[ammonia]] at high temperatures to give a compound called [[borazole]] (B<sub>3</sub>N<sub>3</sub>H<sub>6</sub>), also known as inorganic benzene.

=== Of the several hundred uses of boron compounds, especially notable uses ===

* Boron is an essential plant [[micronutrient]].
* Because of its distinctive green flame, amorphous boron is used in [[Flare (pyrotechnic)|pyrotechnic flares.]]
* Boric acid is an important compound used in textile products. 
* Boric acid is also traditionally used as an insecticide, notably against ants, fleas, and cockroaches.
* [[Borax]] is sometimes found in laundry detergent.
* 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 club]]s and [[fishing rod]]s.
* Boron is used as a melting point depressant in nickel-chromium braze alloys. 
* Boron [[slurry]] is used as an [[energetic material]] with very high energy density like [[rocket fuel]]s and [[jet engine]]s.
* Boron compounds show promise in treating [[arthritis]].

=== Hardest boron compound ===
{{main|Rhenium diboride}}
The hardest Boron compound is created synthetically. [[Rhenium diboride]] (ReB<sub>2</sub>) can actually scratch diamond, giving it a higher than 10 rank in the Mohs scale of mineral hardness and making it one of the three hardest substances known to man - the other two being [[ultrahard fullerite]] and [[aggregated diamond nanorods]].

== History  ==
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, [[Mummy|mummification]] depended upon an ore known as [[natron]], which contained borates as well as some other common salts. Borax [[Ceramic glaze|glaze]]s were used in [[China]] from 300 AD, and boron compounds were used in glassmaking in ancient Rome.

The element was not isolated until [[1808]] by Sir [[Humphry Davy]], [[Joseph Louis Gay-Lussac]], and [[Louis Jacques Thénard]], to about 50 percent purity, by the [[redox|reduction]] of [[boric acid]] with [[sodium]] or [[magnesium]].  These men did not recognize the substance as an element. It was [[Jöns Jakob Berzelius]] in 1824 who identified boron as an element. The first pure boron was produced by the American chemist W. Weintraub in 1909, although this is disputed by some researchers.<ref>{{cite journal| author= | title=| journal= Z. Angew. Phys.| year=1970| pages=277| volume=29}}</ref> 

It is thought that boron plays several biochemical roles in animals, including humans.<ref>http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/bor_0040.shtml</ref>

== Occurrence ==
[[Turkey]] and the [[United States]] are the world's largest producers of boron. Turkey has almost 63% of the world’s boron potential  and  boron  reserves.<ref>{{cite web|url=http://www.byegm.gov.tr/YAYINLARIMIZ/kitaplar/turkiye2006/english/302-303.htm|title=Developments in the Ecomomic Sector (of Turkey)|publisher=Turkish government|accessdate=2007-12-21}}</ref> Boron does not appear in nature in elemental form but is found combined in [[borax]], [[boric acid]], [[colemanite]], [[kernite]], [[ulexite]] and [[borate]]s. Boric acid is sometimes found in [[volcano|volcanic]] spring waters. Ulexite is a [[borate]] [[mineral]] that naturally has properties of [[fiber optics]].

[[Image:Borax crystals.jpg|thumb|100px|right|Borax crystals]]

Economically important sources are from the [[ore]] rasorite (kernite) and tincal (borax ore) which are both found in the [[Mojave Desert]] of [[California]], with borax being the most important source there. The largest [[borax]] deposits are found in Central and Western [[Turkey]] including the provinces of [[Eskişehir]], [[Kütahya]] and [[Balıkesir]].

Even a  boron-containing natural [[antibiotic]], [[boromycin]], isolated from [[streptomyces]], is known.<ref>{{cite journal| author=R. Hütter, W. Keller-Schien, F. Knüsel, [[Vladimir Prelog|V. Prelog]] , G. C. Rodgers jr., P. Suter, G. Vogel, W. Voser, H. Zähner  | title=Stoffwechselprodukte von Mikroorganismen. 57. Mitteilung. Boromycin| journal=Helv. Chim. Acta. | year= 1967| pages=1533–1539| volume=50 | doi = 10.1002/hlca.19670500612}}</ref><ref>{{cite journal| author=J. D. Dunitz, D. M. Hawley, D. Miklo, D. N. J. White, Yu. Berlin, R. Marui, [[Vladimir Prelog|V. Prelog]]  | title=Structure of boromycin | journal= Helv. Chim. Acta.| year= 1971| pages=1709–1713| volume=54| doi = 10.1002/hlca.19710540624}}</ref>

Pure elemental boron is not easy to prepare. The earliest methods used involve reduction of [[boric oxide]] with metals such as [[magnesium]] or [[aluminium]]. However the product is almost always contaminated with metal [[boride]]s. (The reaction is quite spectacular though.)  Pure boron can be prepared by reducing volatile boron halogenides with [[hydrogen]] at high temperatures.  The highly pure boron, for the use in semiconductor industry, is produced by the decomposition of [[diborane]] at high temperatures and then further purified with the [[Czochralski process]].

=== Food ===
Boron occurs in all foods produced from 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 reduce excretion of calcium by 44%, and activate estrogen and vitamin D.

The US [[National Institute of Health]] quotes this source:
:Total daily boron intake in normal [[diet (nutrition)|human diet]]s ranges from 2.1–4.3 mg boron/kg body weight (bw)/day. "Total boron". Zook EG and Lehman J. ''J. Assoc. Off Agric. Chem''. 48: 850-5 (1965).

''See also: [[:category:Borate minerals|Borate minerals]].''

=== Analytical quantification ===
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.

== Isotopes ==   
Boron has two naturally-occurring and stable [[isotope]]s, <sup>11</sup>B (80.1%) and <sup>10</sup>B (19.9%). The mass difference results in a wide range of δ<sup>11</sup>B values in natural waters, ranging from -16 to +59. There are 13 known isotopes of boron, the shortest-lived isotope is <sup>7</sup>B which decays through [[proton emission]] and [[alpha decay]]. It has a [[half-life]] of 3.26500x10<sup>-22</sup> [[Second|s]]. Isotopic fractionation of boron is controlled by the exchange reactions of the boron species B([[oxygen|O]][[hydrogen|H]])<sub>3</sub> and B(OH)<sub>4</sub>. Boron isotopes are also fractionated during [[mineral crystallization]], during H<sub>2</sub>O phase changes in [[hydrothermal]] systems, and during hydrothermal alteration of [[Rock (geology)|rock]]. The latter effect species preferential removal of the <sup>10</sup>B(OH)<sub>4</sub> [[ion]] onto clays results in solutions enriched in <sup>11</sup>B(OH)<sub>3</sub> may be responsible for the large <sup>11</sup>B enrichment in seawater relative to both [[ocean]]ic crust and [[continent]]al crust; this difference may act as an [[isotopic signature]].

The exotic <sup>17</sup>B exhibits a [[Nuclear halo]].   

== 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.

== See also ==
*[[Boron deficiency]]
*[[Boronic acid]]
*[[Suzuki coupling]]
*[[Hydroboration-oxidation reaction]]

== References ==
{{reflist|2}}
*[http://periodic.lanl.gov/elements/5.html Los Alamos National Laboratory &ndash; Boron]
<!--{{cite journal 
 | title = Boron. I. Preparation and Properties of Pure Crystalline Boron
 | author = A. W. Laubengayer, D. T. Hurd, A. E. Newkirk, J. L. Hoard
 | journal =  J. Am. Chem. Soc.
 | volume = 65
 | issue =  10 
 | pages = 1924-1931
 | year = 1943
 | url = 
 | doi = 10.1021/ja01250a036}}-->

== External links ==
{{Commons|Boron}}
{{wiktionary|boron}}
* [http://www.du.edu/~jcalvert/phys/boron.htm Boron]
* [http://www.compchemwiki.org/index.php?title=Boron Computational Chemistry Wiki]
* [http://www.inchem.org/documents/ehc/ehc/ehc204.htm Environmental Health Criteria 204: Boron (1998)] by the [[International Programme on Chemical Safety|IPCS]].
* [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]
[[Category:Chemical elements]]
[[Category:Dietary minerals]]
[[Category:Metalloids]]
[[Category:Boron]]
[[Category:Pyrotechnic fuels]]
[[Category:Rocket fuels]]
[[Category:Neutron poisons]]
[[Category:Nuclear fusion fuels]]

[[af:Boor (element)]]
[[ar:بورون]]
[[ast:Boru]]
[[bn:বোরন]]
[[be:Бор, хімічны элемент]]
[[bs:Bor (element)]]
[[bg:Бор (елемент)]]
[[ca:Bor]]
[[cs:Bor (prvek)]]
[[co:Boru]]
[[cy:Boron]]
[[da:Bor (grundstof)]]
[[de:Bor]]
[[et:Boor]]
[[el:Βόριο]]
[[es:Boro]]
[[eo:Boro]]
[[eu:Boro]]
[[fa:بور]]
[[fr:Bore]]
[[fur:Bôr]]
[[ga:Bórón]]
[[gl:Boro (elemento)]]
[[ko:붕소]]
[[hy:Բոր]]
[[hi:बोरोन]]
[[hr:Bor (element)]]
[[io:Borono]]
[[id:Boron]]
[[is:Bór]]
[[it:Boro]]
[[he:בורון]]
[[sw:Boroni]]
[[ku:Boron]]
[[la:Borium]]
[[lv:Bors]]
[[lb:Bor]]
[[lt:Boras]]
[[jbo:jicmrboro]]
[[hu:Bór]]
[[mk:Бор (хемиски елемент)]]
[[ml:ബോറോണ്‍]]
[[mi:Pūtiwha]]
[[ms:Boron]]
[[nah:Xacoiztatl]]
[[nl:Boor (element)]]
[[ja:ホウ素]]
[[no:Bor (grunnstoff)]]
[[nn:Grunnstoffet bor]]
[[nov:Bore]]
[[oc:Bòr]]
[[uz:Bor (unsur)]]
[[nds:Bor (Element)]]
[[pl:Bor]]
[[pt:Boro]]
[[ro:Bor (element)]]
[[qu:Boru]]
[[ru:Бор (элемент)]]
[[scn:Boru]]
[[simple:Boron]]
[[sk:Bór]]
[[sl:Bor (element)]]
[[sr:Бор (хемијски елемент)]]
[[sh:Bor (element)]]
[[fi:Boori]]
[[sv:Bor]]
[[ta:போரான்]]
[[th:โบรอน]]
[[vi:Bo]]
[[tg:Бор]]
[[tr:Bor (element)]]
[[uk:Бор]]
[[zh-yue:硼]]
[[zh:硼]]