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.
MineralFormulaDensityHardnessCrystal 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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