Boron (B)

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Boron 5Pb10.811


Boron was discovered in 1808 by L.J. Lussac and L.J. Thenard in Paris, France and Sir Humphry Davy in London, England.

[Arabic, buraq]

French: bore
German: Bor
Italian: boro
Spanish: boro

Description: Boron is a non-metal element with several forms - the most common is amorphous boron, which is a dark powder, unreactive to oxygen, water, acids and alkalis. It reacts with metals to form borides. Boron compounds are used in borosilicate glass, detergents and fire-retardants.

Further Materials properties

 

Crystal structure:

(cell dimensions/pm), space group,
Tetragonal (a=874.0; c=506), P42/nnm
α-B rhombohedral (a= 506.7, α=58° 4'), R3m
β-B rhombohedral (a= 1014.5, α=65° 12'), R3m, R32, R3m
Orthorhombic (a=1015, b=895, c=1790)
Monoclinic (a=1013, b=893, c=1786, α=90°, β=90°, γ=90°) or triclinic
Hexagonal (a=1198, c=954)

X-ray diffractions mass absorption coefficients: CuKa 2.39 (µ/r) / cm2g-1
MoKa 0.392 (µ/r) / cm2g-1
Neutron scattering length: 0.535 b/10-12 cm
Thermal neutron capture cross-section: 767 sa / barns
Density: 2340 (β-rhomb.) kg/m-3 [293 K]
Melting point: 2299.85 °C / 2573 °K 
Boiling point: 3657.85 °C / 3931 °K
Molar volume: 4.62 cm3
Thermal conductivity: 27.0 [300 K] Wm-1K-1
Coefficient of linear thermal expansion: 5 x 10-6 K-1
Electrical resistivity: 18 000 [273 K] Ωm
Mass magnetic susceptibility: -7.8 x 10-9  (s) kg-1m3
Radi: B3+ 23; atomic 83; covalent 88; van der Waals 208
Electronegativity: 2.04 (Pauling); 2.01 (Allred); 4.29 eV (absolute)
Effective nuclear charge: 2.60 (Slater); 2.42 (Clementi); 2.27(Froese-Fischer)
Number of Isotopes (incl. nuclear isomers): 6
Isotope mass range: 8 -> 13

 

 


Biological data

 

Biological role: Essential to plants; toxic in excess
Toxicity  
Toxic intake: 5 g (boric acid)
Lethal intake: 10 - 20 g (boric acid). LD50 (boric acid, oral, rat) = 2.66g kg-1
Hazards: Boric acid and borates are a human poison in excess, althrough once used in medicines.
Level in humans  
Blood: 0.13 mg dm-3
Bone: 1.1 - 3.3 ppm
Liver: 0.4 - 3.3 ppm
Muscle: 0.33 - 1 ppm
Daily dietary intake: 1 - 3 mg
Total mass of element in average
[70 kg] person:
18 mg

 

Geological data

 

Minerals:
MineralFormulaDensityHardnessCrystal apperance
Borax  Na2B4O5(OH)4.8H2O  1.715  2 - 2.5  mon., vit. /res./ earthy colourless
Colemanite  CaB2O4(OH)3.H2O  2.423  4.5  mon., vit./adam. colourless
Datolite  CaBSiO4(OH)  3.0  5 - 5.5  mon., vit. white
Kernite  Na2B4O6.(OH)2.3H2O  1.908  2.5  mon. vit. colourless
Ulexite  NaCaB5O6(OH)6.5H2O  1.955  2.5  tric., silky/ vit. colourless

 

Chief ores: kernite, borax, ulexite, colemanite
World production: 1 x 106 (B2O3) tonnes/year
Main mining areas: ulexite in USA, Tibet, Chile; colemanite in USA, Turkey
Reserves: 270 x 106 tonnes as B2O3  
Specimen: available as crystals, pieces or powder. Safe. Safe.

 

Abundances  
Sun: 2.63 x 105 (relative to H = 1 x 1012)
Earth's crust: 950 ppm
Seawater 4.41 ppm
Residence time: 1 x 107 years
Classification: accumulating 
Oxidation state: III

  Source: Emsley, J. (1998) The Elements (3rd Edition)

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