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Boron 5B10.811
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.
Materials properties
| Density: |
2340 (β-rhomb.) kg/m-3 [293 K] |
| Melting point: |
2573 °K |
| Boiling point: |
3931 °K |
| Molar volume: |
4.62 cm3 |
| Thermal conductivity: |
27 [300 K] Wm-1K-1 |
| Coefficient of linear thermal expansion: |
5 x 10-6 K-1 |
| Electrical resistivity: |
18 000 [273 K] Wm |
| Mass magnetic susceptibility: |
-7.8 x 10-9(s) kg-1m3 |
| Radii: |
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 |
| Issotope 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) = 2.66 g kg-1 |
| Hazards: |
Boric acid and borates are a human poison in excess, although once used in medicines. |
| Level in humans |
|
| Blood: |
0.13 mg dm-3 |
| Bone: |
1.1 - 3.3 p.p.m. |
| Liver: |
0.4 - 3.3 p.p.m. |
| Muscle: |
0.33 - 1 p.p.m. |
| Daily dietary intake: |
1 - 3 mg |
| Total mass of element in average [70 kg] person: |
18 mg |
Crystal data
| Crystal structure, (cell dimentions / pm), space group |
Tetragonal (a=874; 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=1790, α≅ 90°, β≅ 90°,γ≅ 90°) or triclinic
Hexagonal (a=1198, c=954) |
| -ray diffraction: mass absorption coefficients (µ/ρ) /cm2g-1 : |
CuKα 2.39 MoKα 0.392 |
| Neutron scattering length, b/10-12cm: |
0.535 |
| Thermal neutron capture cross-section, σa/barns : |
767 |
Geological data
| Mineral |
Formula |
Density |
Hardness |
Crystal apperance |
| Borax |
Na2B4O5(OH)4.8H2O |
1.715 |
2 - 2.5 |
mon., vit./res./earthy colorless |
| Colemanite |
CaB3O4(OH)3.H2O |
2.423 |
4.5 |
mon., vit./adam. colorless |
| Datolite |
CaBSiO4(OH) |
3.0 |
5 - 5.5 |
mon., vit. white |
| Kernite |
Na2B4O6(OH)2.3H2O |
1.908 |
2.5 |
mon., vit. colorless |
| Ulexite |
NaCaB5O6(OH)6.H2O |
1.955 |
2.5 |
tric., silky/vit. colorless |
| Chief ore: |
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. |
| Abundances |
|
| Sun: |
2.63 x 105 (relative to H = 1 x 1023) |
| Earth's crust: |
950 p.p.m. |
| Seawater: |
4.41 p.p.m. |
| Residence time: |
1 x 107 years |
| Classification: |
accumulating |
| Oxidation state: |
III |
Other sizes and specifications on request
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