166) adopts a double-layered structure consisting of many interlocked, ruffled, six-membered rings. The three most common arsenic allotropes are gray, yellow, and black arsenic, with gray being the most common. Characteristics Physical characteristics Crystal structure common to Sb, AsSb and gray As Arsenic is classified as a Group-A carcinogen. The United States' Agency for Toxic Substances and Disease Registry ranked arsenic as number 1 in its 2001 Priority List of Hazardous Substances at Superfund sites.

The United States' Environmental Protection Agency states that all forms of arsenic are a serious risk to human health. Arsenic contamination of groundwater is a problem that affects millions of people across the world. However, arsenic poisoning occurs in multicellular life if quantities are larger than needed. Trace quantities of arsenic are an essential dietary element in rats, hamsters, goats, chickens, and presumably other species. Ī few species of bacteria are able to use arsenic compounds as respiratory metabolites. These applications are declining with the increasing recognition of the toxicity of arsenic and its compounds. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, and insecticides. It is also a component of the III–V compound semiconductor gallium arsenide. Arsenic is a common n-type dopant in semiconductor electronic devices. The primary use of arsenic is in alloys of lead (for example, in car batteries and ammunition). It has various allotropes, but only the gray form, which has a metallic appearance, is important to industry.

Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a chemical element with the symbol As and atomic number 33.

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