Cacl₂-calciums symbol is ca, and chlorines symbol is cl. calcium is an alkaline earth metal (2, 2a, or iia), which means it forms a +2 ion. chlorine is a halogen (17, 7b, or viia) and forms a -1 ion. the compound would be ionic (formed from elements on opposite sides of the periodic table): ca+2cl-1. writing the superscript of one ion as the subscript of the other gives the correct formula: l2, or more properly, cacl2. choice a. implies three elements: calcium, carbon, and an unknown element known as l.