These chemical formulas represent different compounds containing calcium ions. Calcium oxide (CaO) is produced when calcium carbonate (CaCO3) is heated, and when mixed with water, it forms calcium hydroxide (Ca(OH)2). Calcium chloride (CaCl2) and calcium nitrate (Ca(NO3)2) are salts that contain calcium ions bonded to chlorine and nitrate ions, respectively. Calcium oxide (CaO) and calcium carbonate (CaCO3) are also compounds that contain calcium ions.