Definition: Arsenic was a chemical element with an atomic number of 32, found in arsenic dioxide or in soil samples. It's considered poisonous due to its chemical properties. Definition: Arsenic (As) is a toxic metal that occurs naturally as arsenic dioxide in soil and groundwater. It's also produced by industrial processes and from burning coal, which can produce more than twice the amount of arsenic found at home. Arsenic is a colorless, odorless, tasteless, alkaline earth element with an atomic number of 32. Its chemical symbol is Ag.