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Arsenic - As

CAS: 7740-38-2
Description: Gray, brittle, non-metallic flakes
Classification: Metalloid
Date of Discovery: Known to the ancients
Discoverer: Unknown
Name Origin: Greek arsenikon, yellow orpiment; Latin arsenicum

Atomic Number: 33
Number of Neutrons: 42
Atomic Mass: 74.92159(2) amu
Melting Point: 817 °C
Boiling Point: 614 °C
Density (293 K): 5.73 g/cm3
Atomic volume: 13.1 cm3/mol
Electrical resistivity: 0.0345 10-6/cm Ohm Symbol
Thermal conductivity: 0.500 W/cmK
Enthalpy of atomization: 301.25 kJ/mol
Enthalpy of vaporization: 34.760 kJ/mol
Enthalpy of fusion: 24.44 kJ/mol
Specific heat capacity: 0.33 J/gK 		Energy levels: 2-8-18-5
Electron configuration: [Ar]3d104s24p3
Crystal Structure: Rhombohedral
Atomic radius: 1.33 Å
Covalent radius: 1.20 Å
Oxidation States: -3, 0, +3, +5
Electronegativity, Pauling: 2.18
Electron affinity: 0.81 eV
First ionization energy: 9.81 eV
2nd ionization energy: 18.633 eV
3rd ionization energy: 28.351 eV
Polarizability: 4.31 10-24cm3
Isotope Natural Abundance Atomic Mass Half-life Decay Mode Spin
65As 64.9495 Alpha Symbol0.19 s Beta Symbol+
66As 65.94410 95.8 ms Beta Symbol+
67As 66.9392 42 s Beta Symbol+; EC 5/2-
68As 67.9368 2.53 m Beta Symbol+ 3+
69As 68.93228 15.2 m Beta Symbol+; EC 5/2-
70As 69.93093 52.6 m Beta Symbol+; EC 4+
71As 70.927114 2.72 d Beta Symbol+; EC 5/2-
72As 71.926753 26.0 h Beta Symbol+ 2-
73As 72.923825 80.3 d EC 3/2-
74As 73.923829 17.78 d Beta Symbol+; EC; Beta Symbol- 2-
75As 100. 74.921597 Stable 3/2-
76As 75.922394 26.3 h Beta Symbol- 2-
77As 76.920648 38.8 h Beta Symbol- 3/2-
78As 77.92183 1.512 h Beta Symbol- 2-
79As 78.92095 9.0 m Beta Symbol- 3/2-
80As 79.92258 16 s Beta Symbol- 1+
81As 80.92213 33 s Beta Symbol- 3/2-
82As 13.7 s Beta Symbol- 5-
82As 81.9246 19 s Beta Symbol- 1+
83As 82.9250 13.4 s Beta Symbol-
84mAs 0.6 s Beta Symbol-
84As 83.9291 4 s Beta Symbol-, n 1-
85As 84.9318 2.03 s Beta Symbol-, n 3/2-
86As 85.9362 0.95 s Beta Symbol-, n
87As 86.9396 0.49 s Beta Symbol-, n
Elemental arsenic occurs in two solid modifications: yellow (specific gravity, 1.97), and gray or metallic. Gray arsenic is the ordinary, stable form, with several other allotropic forms reported in literature. It is believed that Albertus Magnus obtained the element in 1250 A.D. In 1649 Schroeder published two methods of preparing the element. It is found native, in the sulfides realgar (AsS) and orpiment (As2S3), as arsenides and sulfarsenides of heavy metals, as the oxide, and as arsenates. Mispickel, arsenopyrite, (FeSAs) is the most common mineral from which, on heating, the arsenic sublimes leaving ferrous sulfide. The element is a steel gray, very brittle, crystalline, semimetallic solid; it tarnishes in air, and when heated is rapidly oxidized to arsenous oxide (As2O3) with the odor of garlic. Arsenic and its compounds are poisonous. Arsenic is used in bronzing, pyrotechny, and for hardening and improving the sphericity of shot. The most important compounds are white arsenic (As2O3), the sulfide, Paris green 3Cu(AsO2)2· Cu(C2H3O2)2, calcium arsenate, and lead arsenate; the last three have been used as agricultural insecticides and poisons. Marsh's test makes use of the formation and ready decomposition of arsine (AsH3). Arsenic is available in high-purity form. It is finding increasing uses as a doping agent in solid-state devices such as transistors. Gallium arsenide is used as a laser material to convert electricity directly into coherent light. Natural arsenic is made of one isotope 75As. Twenty-five other radioactive isotopes and isomers are known.
LINKS:

AMM Online - Arsenic Profile
Arsenic
Arsenic Affects the Whole Body
Arsenic and Health
ATSDR - Public Health Statement: Arsenic
Beneficial actions
EcoIndiana: Arsenic
Minerals Containing Arsenic
NRC/NAS Report on Arsenic in Drinking Water
Study and Remediation of Chronic Arsenic poisoning


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Sources for the information on this website include:
Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998.
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