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Arsenic (As)
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Arsenic 33As74.92
Probably first isolated by Albertus Magnus (1193-1280).
[Greek: arsenikon = yellow orpiment, Latin: arsenicum]
French: arsenic
German: Arsen
Italian: arsenico
Spanish: arsénico
Description: Arsenic is a metalloid element with two main forms. Gray α-arsenic is metallic and is brittle, tarnishes and burns in oxygen. Arsenic resists attack by water, ordinary acids and alkalis. However, it reacts with hot acids and molten NaOH. Arsenic is used in alloys, semiconductors, pesticides, wood preservatives and glass.
Further Materials properties
| Crystal structure: |
(cell dimensions/pm), space group, α-As rhombohedral (a=413.18, α=54° 10'), R3m, metallic form β-As hexagonal (a=376.0, c=10.548), yellow grey amorphous, T (α -> β) = 501 K; T(β -> grey) = room temperature |
|---|---|
| X-ray diffractions mass absorption coefficients: | CuKa 83.4 (µ/r) / cm2g-1 MoKa 69.7 (µ/r) / cm2g-1 |
| Neutron scattering length: | 0.658 b/10-12 cm |
| Thermal neutron capture cross-section: | 4.30 sa / barns |
| Density: | 5780 (α) 4700 (β) kg/m-3 [293 K] |
| Melting point: | 816.85 °C / 1090 °K (α, under pressure) |
| Boiling point: | 615.85 °C / 889°K |
| Molar volume: | 12.95 (α) 15.9 (β) cm3 |
| Thermal conductivity: | 50.0 (α) [300 K] Wm-1K-1 |
| Coefficient of linear thermal expansion: | 4.7 x 10-6 K-1 |
| Electrical resistivity: | 26 x 10-8 [273 K] Ωm |
| Mass magnetic susceptibility: | -9.17 x 10-10(α). -3.97 x 10-9 (β) kg-1m3 |
| Radi: | As5+ 46, As3+ 69; atomic 125; covalent 121; van der Waals 200 |
| Electronegativity: | 2.18 (Pauling); 2.20 (Allred); 5.3 eV (absolute) |
| Effective nuclear charge: | 6.30 (Slater); 7.45 (Clementi); 8.98(Froese-Fischer) |
| Number of Isotopes (incl. nuclear isomers): | 22 |
| Isotope mass range: | 67 -> 87 |
Biological data
| Biological role: | Essential to some species including humans |
|---|---|
| Toxicity | |
| Toxic intake: | 5 - 50 mg |
| Lethal intake: | > 50 - 300 mg, LD50 (oral) = 100mg |
| Hazards: | Arsenic salts and arsine gases are very poisonous. In small doses arsenic acts to stimulate metabolism, but it is carcinogetic and possibly teratogenic. |
| Level in humans | |
| Blood: | 0.0017-0.09 mg dm-3 |
| Bone: | 0.08 - 1.6 ppm |
| Liver: | 0.023 - 1.61 ppm |
| Muscle: | 0.009 - 0.65 ppm |
| Daily dietary intake: | 0.04 - 1.4 mg |
| Total mass of element in average [70 kg] person: |
7 mg |
Geological data
| Minerals: | A little native arsenic occurs naturally as microcrystalline masses, found in Siberia, Germany, France, Italy, Romania and the USA. | |||
|---|---|---|---|---|
| Mineral | Formula | Density | Hardness | Crystal apperance |
| Arsenopyrite | FeAsS | 6.07 | 5.5 - 6 | tet., met. silvery-white |
| Conichalcite | CaCu(AsO4)(OH) | 4.33 | 4.5 | orth., vitreous green |
| Enagite | Cu3AsS4 | 4.45 | 3 | orth., met. grey-black |
| Löllingite | FeAs2 | 7.40 | 5 - 5.5 | orth., met. white |
| Olivenite | Cu2(ASO4)(OH) | 4.46 | 3 | mon., adam./ vitreous green |
| Orpiment | As2S3 | 3.49 | 1.5 - 2 | mon., trans. resinous golden |
| Realgar | β-As4S4 | 3.5 | 1.5 - 2 | mon., res. red-orange |
| Chief ore: | arsenopytite, realgar, orpiment. |
|---|---|
| World production: | 47000 (As2O3) tonnes/year |
| Main mining areas: | not much mined as such because more than required is produced as a by-product of refining certain sulfide ores. |
| Reserves: | n.a. |
| Specimen: | available as pieces or powder. DANGER! |
| Abundances | |
|---|---|
| Sun: | n.a. (relative to H = 1 x 1012) |
| Earth's crust: | 1.5 ppm |
| Seawater | |
| Atlantic surface: | 1.45 x 10-3 ppm |
| Atlantic deep: | 1.53 x 10-3 ppm |
| Pacific surface: | 1.45 x 10-3 ppm |
| Pacific deep: | 1.75 x 10-3 ppm |
| Residence time: | 90 000 years |
| Classification: | As(III) scavenged, As(V) recycled |
| Oxidation state: | III but mainly V |
Source: Emsley, J. (1998) The Elements (3rd Edition)
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