User:Ayirriya/sandbox

BORON

Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder, essential to plant growth and of wide industrial application.

Chemical Properties of Boron

Group	13 (Boron Group)

Melting point	2349K

Period	2

Boiling point	4200K

Block	p-block

Density (g cm−3)	2.08 (when liquid)

Atomic number	5

Electron configuration	[He]2s22p1

State at 20°C	Solid

Properties

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 Earth’s 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. Sassolite—natural boric acid—occurs especially in Italy.

Occurances

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. 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. 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.

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. In nature, boron consists of a mixture of two stable isotopes—boron-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. 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.

Uses''

•	Amorphous boron is used as a rocket fuel igniter and in pyrotechnic flares. It gives the flares a distinctive green colour.

•	The most important compounds of boron are boric (or boracic) acid, borax (sodium borate) and boric oxide. These can be found in eye drops, mild antiseptics, washing powders and tile glazes. Borax used to be used to make bleach and as a food preservative.

•	Boric oxide is also commonly used in the manufacture of borosilicate glass (Pyrex). It makes the glass tough and heat resistant. Fibreglass textiles and insulation are made from borosilcate glass.

•	Sodium octaborate is a flame retardant.

•	The isotope boron-10 is good at absorbing neutrons. This means it can be used to regulate nuclear reactors. It also has a role in instruments used to detect neutrons.

References

•	https://www.rsc.org/periodic-table/element/5/boron.

•	Britannica, T. Editors of Encyclopaedia (2023, March 2). boron. Encyclopaedia Britannica. https://www.britannica.com/science/boron-chemical-element.