mercuryI

Mercury(I), also called mercurous, describes mercury in the +1 oxidation state. In most compounds the mercury atoms exist as a diatomic cation, Hg2^2+, in which two mercury atoms share a mutual metal–metal bond. This Hg2^2+ unit is the characteristic feature of mercurous chemistry, distinguishing it from mercury(II) compounds in which each mercury is present as Hg2+ ions.

Mercurous salts are typically less stable in aqueous solution than their mercuric counterparts and many mercurous salts are white or colorless solids. A well-known mercurous compound is mercurous chloride, commonly called calomel (Hg2Cl2). Other examples include mercurous nitrate (Hg2(NO3)2) and mercurous sulfate (Hg2SO4).

Mercurous compounds have practical uses: calomel was used historically as a laxative and antiseptic, and calomel electrodes in electrochemistry use Hg2Cl2; mercurous salts have also been explored as pigments and in some dental materials in the past.

Safety: Mercury(I) compounds are toxic; exposure can cause neurological and kidney damage. They are environmentally hazardous and require careful handling, containment, and disposal to prevent mercury release and exposure.