Arsenic was discovered about 1250. Like antimony and bismuth, arsenic occurs in nature sulfide ores, As₂S₃, orpiment. It can also be found in ores of various metals such as copper, lead, silver and mercury.

Arsenic is classed as a semimetal. When heated, it sublimes.

Although all arsenic compounds are poisonous, some of its compounds were once medicines. But most of their uses in this area are now banned. Although 0.1 gram doses of arsenic are lethal to humans, traces of arsenic can stimulate the production of red blood cells.