arsenikum

Arsenicum, or arsenic, is a chemical element with symbol As and atomic number 33. It is widely described as a metalloid. It shows several allotropes, with gray arsenic being the most stable form at room temperature; a more reactive yellow form exists as well. In older Latin texts the element is referred to as arsenicum.

In nature, arsenic is common in minerals such as arsenopyrite (FeAsS), realgar (As4S4), and orpiment (As2S3). Native arsenic is rare. It is often obtained by roasting arsenic-bearing minerals to release arsenic trioxide, which is then reduced to metal or used directly in compounds.

Chemically, arsenic exhibits oxidation states -3, +3, and +5 and forms various compounds such as arsenic trioxide As2O3 and arsenates and arsenites. Arsenic forms arsenides with metals and is an essential component of many semiconductor materials (for example gallium arsenide, GaAs).

Historically, arsenic has been used as a pigment (orpiment) and in medicine; notably arsenic-containing drugs such as arsphenamine were used to treat syphilis in the early 20th century. It remains widely used in industry in small amounts, including in glassmaking and as a wood preservative; however, many uses have declined due to toxicity.

Arsenic and its inorganic compounds are highly toxic and carcinogenic, with exposure occurring via water, air, or consumer products. Safety measures include proper handling, monitoring, and regulatory controls. The element is a central example of environmental and public health concerns related to trace metalloid contaminants.