Editing Period 2 element (section)

===Boron===
{{main article|Boron}}
[[File:Bor 1.jpg|thumb|left|150px|Boron chunks]]

Boron (B) is the chemical element with atomic number 5, occurring as <sup>10</sup>B and <sup>11</sup>B. At standard temperature and pressure, boron is a [[trivalent]] [[metalloid]] that has several different [[allotropy|allotropes]]. [[Amorphous]] boron is a brown powder formed as a product of many chemical reactions. [[Crystalline]] boron is a very hard, black material with a high melting point and 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 most common. Boron has a density of 2.34<sup>−3</sup>.<ref name=web>[http://www.webelements.com/boron/  Boron] at WebElements.</ref> Boron's most common [[isotope]] is <sup>11</sup>B at 80.22%, which contains 5 protons and 6 neutrons. The other common isotope is <sup>10</sup>B at 19.78%, which contains 5 protons and 5 neutrons.<ref name=rem>[http://www.rareearth.org/boron_properties.htm Properties] of boron.</ref> These are the only stable isotopes of boron; however [[Isotopes of boron|other isotopes]] have been synthesised. Boron forms covalent bonds with other [[Nonmetal (chemistry)|nonmetal]]s and has [[oxidation state]]s of 1, 2, 3 and 4.<ref>{{cite web |url=http://bernath.uwaterloo.ca/media/78.html |format=PDF |title=Fourier Transform Spectroscopy: B<sup>4</sup>Σ<sup>−</sup>−X<sup>4</sup>Σ<sup>−</sup> |author1=W.T.M.L. Fernando |author2=L.C. O'Brien |author3=P.F. Bernath |publisher=University of Arizona, Tucson |access-date=2007-12-10 }}{{Dead link|date=August 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite web |url=http://bernath.uwaterloo.ca/media/125.html |format=PDF |title=Infrared Emission Spectroscopy of BF and AIF |author=K.Q. Zhang, B.Guo, V. Braun, M. Dulick, P.F. Bernath |access-date=2007-12-10 }}{{Dead link|date=August 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><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> |access-date=2007-12-10 |publisher=Landol Börnstein Substance/Property Index}}</ref>
Boron does not occur naturally as a free element, but in compounds such as [[borate]]s. The most common sources of boron are [[tourmaline]], [[borax]], Na<sub>2</sub>B<sub>4</sub>O<sub>5</sub>(OH)<sub>4</sub>·8H<sub>2</sub>O, and [[kernite]], Na<sub>2</sub>B<sub>4</sub>O<sub>5</sub>(OH)<sub>4</sub>·2H<sub>2</sub>O.<ref name=web/> it is difficult to obtain pure boron. It can be made through the [[magnesium]] [[redox|reduction]] of [[boron trioxide]], B<sub>2</sub>O<sub>3</sub>. This oxide is made by melting [[boric acid]], B(OH)<sub>3</sub>, which in turn is obtained from borax. Small amounts of pure boron can be made by the [[thermal decomposition]] of boron bromide, BBr<sub>3</sub>, in hydrogen gas over hot [[tantalum]] wire, which acts as a [[catalyst]].<ref name=web/> The most commercially important sources of boron are: [[sodium tetraborate]] pentahydrate, Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub> · 5H<sub>2</sub>O, which is used in large amounts in making insulating [[fiberglass]] and [[sodium perborate]] [[Bleach (chemical)|bleach]]; [[boron carbide]], a [[ceramic]] material, is used to make armour materials, especially in [[bulletproof vest]]s for soldiers and police officers; [[orthoboric acid]], H<sub>3</sub>BO<sub>3</sub> or boric acid, used in the production of textile [[fiberglass]] and [[flat panel display]]s; sodium tetraborate decahydrate, Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub> · 10H<sub>2</sub>O or borax, used in the production of adhesives; and the isotope boron-10 is used as a control for nuclear reactors, as a shield for nuclear radiation, and in instruments used for detecting neutrons.<ref name=rem/>

Boron is an essential plant [[micronutrient]], required for cell wall strength and development, cell division, seed and fruit development, sugar transport and hormone development.<ref>{{cite journal
 | title = Functions of Boron in Plant Nutrition
 | first = Dale G.
 | last = Blevins
 |author2=Lukaszewski, Krystyna M.
  | journal = Annual Review of Plant Physiology and Plant Molecular Biology
 | volume = 49
 | pages = 481–500
 | year = 1998
 | doi = 10.1146/annurev.arplant.49.1.481
 | pmid = 15012243 }}</ref> However, high soil concentrations of over 1.0 [[parts per million|ppm]] can cause necrosis in leaves and poor growth. Levels as low as 0.8 ppm can cause these symptoms to appear in plants particularly boron-sensitive. Most plants, even those tolerant of boron in the soil, will show symptoms of boron toxicity when boron levels are higher than 1.8 ppm.<ref name=rem/> In animals, boron is an [[ultratrace element]]; in human diets, daily intake ranges from 2.1 to 4.3&nbsp;mg boron/kg body weight (bw)/day.<ref>{{cite journal | title = 850-5 |vauthors=Zook EG, Lehman J| journal = J. Assoc. Off Agric. Chem | volume = 48 | year = 1965}}</ref> It is also used as a supplement for the prevention and treatment of osteoporosis and arthritis.<ref>{{cite web | url = http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/bor_0040.shtml
| title = Boron | access-date = 2008-09-18 | publisher = PDRhealth |archive-url = https://web.archive.org/web/20071011101928/http://pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/bor_0040.shtml |archive-date=October 11, 2007 }}</ref>