Arsenic

General properties
Name, symbol, number	arsenic, As, 33
Element category	metalloid
Group, period, block	15, 4, p
Standard atomic weight	74.92160(2)
Electron configuration	[Ar] 4s2 3d10 4p3 2, 8, 18, 5
History
Discovery	Early Bronze Age (2500 BC)
First isolation	Albertus Magnus (1250)

Arsenic is a chemical element with symbol A sand atomic number 33. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250. Arsenic 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. These applications are declining, however.

Arsenic is notoriously poisonous to multicellular life, although a few species of bacteria are able to use arsenic compounds as respiratory metabolites. Arsenic contamination of groundwater is a problem that affects millions of people across the world.

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