Arsenic is a chemical element with symbol As and atomic number 33. It is a metalloid. It can exist in various allotropes, although only the gray form has important use in industry.
The main use of metallic arsenic is for strengthening alloys of copper and especially lead (for example, in car batteries). Arsenic is a common n-type dopant in semiconductor electronic devices, and the optoelectronic compound gallium arsenide is the most common semiconductor in use after doped silicon. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, and insecticides. However, the element often causes toxicity to multicellular life due to its presence in quantities far larger than needed.