Nomenclature
CAS number: 7440-38-2
Grey arsenic; metallic arsenic; arsen (German).
Description and references
As; at. wt 74.92160; at. no. 33; valences 3,
5. Group VA (15) element, classified as a metalloid. Naturally occurring
isotope (mass number): 75 (100%); known artificial, radioactive isotopes:
66-74; 76-87. Arsenic compds were described and used in antiquity,
especially as poisons; their reduction to the element was known to
medieval alchemists. Albertus Magnus credited with isolation of the
element from the mineral orpiment in ≈1250 a.d.
First precise directions for the prepn of As found in Paracelsus'
writings (ca. 1520). Arsenic probably occurs throughout
the universe. Meteorites reported to contain from 0.0005 to 0.1%
As. Occurrence in the earth's crust: 1.8 ppm. Found in nature to
a small extent as the element; occurs mostly in minerals such as realgar
(As4S4), orpiment (A2S3), arsenolite (As2O3). Commercial sources:
as by-product in flue dusts from smelting copper, lead, cobalt and
gold ores; by melting FeAs2 or FeAsS ores. Prepn of pure
As by reduction with carbon (sugar charcoal) and sublimation in N2: Krepelka, Collect. Czech. Chem. Commun. 2, 255 (1930); E. H. Archibald, The Preparation of Pure
Inorganic Substances (Wiley, New York, 1932) p 269. Other
methods: Schenk in Handbook of Preparative
Inorganic Chemistry vol. 1, G. Brauer, Ed.
(Academic Press, New York, 2nd ed., 1963) pp 591-593. Reviews: Gmelins, Arsenic (8th ed.) 17, 475 pp (1952); Smith, “Arsenic, Antimony and Bismuth” in Comprehensive Inorganic Chemistry vol.
2, J. C. Bailar, Jr. et al., Eds. (Pergamon Press,
Oxford, 1973) pp 547-683; Chemistry of the
Elements, N. N. Greenwood, A. Earnshaw, Eds. (Pergamon
Press, New York, 1984) pp 637-697; S. C. Carapella, Jr. in Kirk-Othmer Encyclopedia of Chemical Technology vol. 3 (John Wiley & Sons, 4th ed., 1992) pp 624-633;
G. O. Doak et al., ibid. pp 633-659. Review
of carcinogenicity studies: IARC Monographs 23, 39-141 (1980); of toxicology and human exposure: Toxicological
Profile for Arsenic (PB2000-108021, 2000) 468 pp. Book:
“The Chemistry of Organic Arsenic, Antimony and Bismuth Compounds,”
S. Patai, Ed. (John Wiley & Sons, New York, 1994) 962 pp.
Properties
Allotropic forms: α-form, metallic, steel-gray,
shiny, brittle, rhombohedral crystal structure; β-form, dark gray,
amorphous sold, d 4.700, transforms to metallic form at 280°. Poisonous. Can be heated to burn in air with bluish flame, giving off an odor
of garlic and dense white fumes of As2O3. Stable
in dry air; loses its luster on exposure to humid air as surface oxidizes,
forming a black modification + As2O3. Brinell
hardness: 147; Mohs' scale: 3.5. d425 5.778. Sublimes760 615° without melting. mp 818° at 36 atm. Heat of vaporization 11.2 kcal/g-atom. Heat of
sublimation 30.5 kcal/g-atom. Heat of fusion: 22.4 kcal/g-atom (Gmelins, loc. cit. pp 135-136).
Also reported as: heat of fusion: 6.620 kcal/g-atom; heat of sublimation
7.63 kcal/g-atom: D. R. Stull, G. C. Sinke, “Thermodynamic Properties
of the Elements” in Advances in Chemistry
Series 18 (A.C.S., Washington, 1956) pp 11,
44. Latent heat of fusion: 27,740 J/mol K. Latent heat of sublimation:
31,974 J/mol K (Carapella). Specific heat (25°) 24.6 J/mol K. Dielectric
constant = 10.23 at 20° and 60 cycles. Electrical and magnetic properties
of crystalline As: Taylor et al., J. Phys. Chem. Solids 26, 69 (1965). Insol in water. Not attacked by cold
H2SO4 or HCl; converted by HNO3 or
hot H2SO4 into arsenous or arsenic acid. A yellow
modification which has no metallic properties has been reported from
sudden cooling of As-vapor. This yellow arsenic is converted back
to the gray modification upon very short exposure to ultraviolet light.Note
In German and other languages Arsenik means arsenic trioxide.Caution
Overexposure to arsenic and arsenic
compounds has been associated with acute and chronic toxicity due
to inhalation or ingestion. Organic forms are usually less harmful
than inorganic forms. Direct contact can cause local irritation and
dermatitis. Overexposure has been associated with an increased risk
of skin, liver, bladder, kidney and lung cancer. See Toxicological
Profile, loc. cit. Inorganic arsenic compounds are listed as
known human carcinogens: Report on Carcinogens,
Eleventh Edition (PB2005-104914, 2004) p III-18.Use
In metallurgy for hardening copper, lead, nonferrous
alloys; automotive body solder. In semiconductor materials. In the
manufacture of low-melting glass. As wood preservative, herbicide,
pesticide.