The chemical formula for barium carbonate is BaCO3. Ba is the symbol of barium and CO3 is the formula for carbonate. The valency of barium is +2 and valency of carbonate is -2. In carbonate, carbon makes one double covalent bond with oxygen and two single covalent bonds with two oxygen atoms. These two oxygen atoms have one-one free electrons and share it to make the covalent bonds with barium. In addition, barium carbonate is also called witherite.