Sometimes referred to in short as inorganic arsenic, inorganic arsenic compound contain arsenic (As) and at least one other element, but no carbon (C). Inorganic arsenic exists in four main chemical forms known as valency or oxidation states. Valency is a measure of the ability of a compound to combine with other elements, such as hydrogen.

The dominant forms are:

• Arsenite, with a valency of 3, also referred to as trivalent arsenic (As (III), As⁺³), and
• Arsenate, with a valency of 5, also referred to as pentavalent arsenic (As (V), As⁺⁵

Inorganic arsenic (compounds) are mainly of geological origin and can be found in groundwater used as drinking water in certain parts of the world.