Editing Boron (section)

==Chemistry of the element==
{{Main|Boron compounds}}

===Preparation===
Elemental boron is rare and poorly studied because the pure material is extremely difficult to prepare. Most studies of "boron" involve samples that contain small amounts of carbon. Very pure boron is produced with difficulty because of contamination by carbon or other elements that resist removal.<ref>{{cite book |last1=Hobbs |first1=Dale Z. |last2=Campbell |first2=Thomas T. |last3=Block |first3=F. E. |title=Methods Used in Preparing Boron |date=1964 |publisher=U.S. Department of the Interior, Bureau of Mines |page=14 |url=https://books.google.com/books?id=37NtbclQPRgC&pg=PA14 |language=en |access-date=25 February 2022 |archive-date=8 March 2024 |archive-url=https://web.archive.org/web/20240308024312/https://books.google.com/books?id=37NtbcongborlQPRgC&pg=PA14#v=onepage&q&f=false |url-status=live }}</ref>

Some early routes to elemental boron involved the reduction of [[boric oxide]] with metals such as [[magnesium]] or [[aluminium]]. However, the product was often contaminated with [[boride]]s of those metals.<ref>{{Cite book |last=Springborg |first=Michael |url=https://books.google.com/books?id=JHMoDwAAQBAJ |title=Chemical Modelling: Applications and Theory Volume 8 |date=1 September 2011 |publisher=Royal Society of Chemistry |isbn=978-1-84973-278-9 |pages=2–3 |language=en}}</ref> Pure boron can be prepared by reducing volatile boron halides with [[hydrogen]] at high temperatures. Ultrapure boron for use in the semiconductor industry is produced by the decomposition of [[diborane]] at high temperatures and then further purified by the [[zone melting]] or [[Czochralski process]]es.<ref name="berger">{{Cite book| title = Semiconductor materials| author = Berger, L. I.| publisher = CRC Press| date = 1996| isbn = 978-0-8493-8912-2| pages = [https://archive.org/details/semiconductormat0000berg/page/37 37–43]| url = https://archive.org/details/semiconductormat0000berg/page/37}}</ref>

===Reactions of the element===
[[Crystalline]] boron is a hard, black material with a melting point of above 2000&nbsp;°C. Crystalline boron is chemically inert and resistant to attack by boiling [[hydrofluoric acid|hydrofluoric]] or [[hydrochloric acid]]. When finely divided, it is attacked slowly by hot concentrated [[hydrogen peroxide]], hot concentrated [[nitric acid]], hot [[sulfuric acid]] or hot mixture of sulfuric and [[chromic acid]]s.<ref name="Laubengayer">{{Cite journal|title = Boron. I. Preparation and Properties of Pure Crystalline Boron| doi =10.1021/ja01250a036|date =1943|first1 =A. W.|last1 = Laubengayer|journal =Journal of the American Chemical Society|volume =65|pages =1924–1931|last2 = Hurd|first2 = D. T.|last3 = Newkirk|first3 = A. E.|last4 = Hoard|first4 = J. L.|issue = 10| bibcode =1943JAChS..65.1924L}}</ref>

Since elemental boron is very rare, its chemical reactions are of little significance practically speaking. The elemental form is not typically used as a precursor to compounds.  Instead, the extensive inventory of boron compounds are produced from borates.<ref name=Brotherton/>

When exposed to air, under normal conditions, a [[Passivation (chemistry)|protective oxide or hydroxide layer]] forms on the surface of boron, which prevents further corrosion.<ref>{{Cite journal |last1=Chintersingh |first1=Kerri-Lee |last2=Schoenitz |first2=Mirko |last3=Dreizin |first3=Edward L. |date=November 2016 |title=Oxidation kinetics and combustion of boron particles with modified surface |url=https://linkinghub.elsevier.com/retrieve/pii/S0010218016302449 |journal=Combustion and Flame |language=en |volume=173 |pages=288–295 |doi=10.1016/j.combustflame.2016.08.027|bibcode=2016CoFl..173..288C }}</ref> The rate of oxidation of boron depends on the crystallinity, particle size, purity and temperature. At higher temperatures boron burns to form [[boron trioxide]]:<ref name="HollemanAF">{{cite book|publisher = Walter de Gruyter|date = 1985|edition = 91–100|pages = 814–864|isbn = 978-3-11-007511-3|title = Lehrbuch der Anorganischen Chemie|first1 = Arnold F.|last1 = Holleman|last2=Wiberg|first2=Egon|last3=Wiberg|first3=Nils|chapter = Bor| language = de}}</ref>
:4 B + 3 O<sub>2</sub> → 2 B<sub>2</sub>O<sub>3</sub>
[[File:Tetraborate-xtal-3D-balls.png|thumb|right|Ball-and-stick model of tetraborate anion, [B<sub>4</sub>O<sub>5</sub>(OH)<sub>4</sub>]<sup>2−</sup>, as it occurs in crystalline borax, Na<sub>2</sub>[B<sub>4</sub>O<sub>5</sub>(OH)<sub>4</sub>]·8H<sub>2</sub>O. Boron atoms are pink, with bridging oxygens in red, and four hydroxyl hydrogens in white. Note two borons are trigonally bonded sp<sup>2</sup> with no formal charge, while the other two borons are tetrahedrally bonded sp<sup>3</sup>, each carrying a formal charge of −1. The oxidation state of all borons is III. This mixture of boron coordination numbers and formal charges is characteristic of natural boron minerals.]]