Arsenic is a metalloid in the 4th period of Group VA. Other members of the group are nitrogen (N), phosphorus (P), antimony (Sb), and bismuth (Bi).
Arsenic combines readily with oxygen, hydrogen, halogens, and sulfur. Although "arsenic" was mentioned in literature of Aristotle's time, the ancient Greeks were probably referring to As2O3. It is believed that Albertus Magnus first obtained the element in 1250 A.D., but the first precise directions for the preparation of arsenic are found in the writings of the great alchemist, Paracelsus, in about 1520 A.D.
The name is derived from Latin arsenicum, which was derived from Greek arsenikon, a word meaning yellow orpiment, a yellow-orange, arsenic-containing ore (As2S3). The symbol As is derived from the name.
Arsenic is found native, in the sufides realgar and orpiment, as arsenides and sulfarsenides of heavy metals, and as oxide and arsenates. Arsenopyrite (FeSAs) is the most common mineral, from which the arsenic sublimes on heating to leave iron(II) sulfide.
Arsenic can also be sublimed from its other ores by roasting and then condensed as the element. Very pure arsenic is prepared by reducing the trioxide with carbon and then subliming the element.
As2O3(s) + 3 C(s) 3 CO(g) + 2 As(s)
Elemental arsenic occurs in three solid modifications: yellow, black, and gray, with densities of 1.97, 4.73, and 5.73 g/ml. Gray arsenic, the ordinary stable form, is a steel gray, very brittle, crystalline, semi-metallic solid; it tarnishes in air and when heated is rapidly oxidized to white clouds of arsenic (III) oxide (As2O3) with the odor of garlic.
Arsenic and its compounds are poisonous -- the "arsenic" of mystery literature (such as the play "Arsenic and Old Lace") is As2O3 -- but some of its organic compounds, such as Salvarsan, are used in medicine and in veterinary medicine. The maximum allowable concentration of arsenic is recommended to be 0.5 mg/m3 of air.
Arsenic is also used in bronzing and pyrotechnics. It is also used for hardening and improving the sphericity of lead shot, which it does by causing the lead to solidify at a lower temperature, hence allowing the shot more time to achieve a spherical shape.
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 being used as agricultural insecticides and poisons and to treat wood to prevent rot.
Marsh's test for arsenic makes use of the formation and ready decomposition or arsine (AsH3), an extremely poisonous gas.
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 in photocells, in light-emitting diodes and as a laser material to convert electricity directly into coherent light.