Question

valency of polyatomic ions

Answer 1

The valencies of the constituent atoms are combined. For example, the polyatomic ion, carbonate, has a formula of CO3. the valence state of oxygen ions is -2 (it’s in Group 16 of the periodic table, two to the left of Group 18, the noble gases: 16–18 = -2). There are 3 oxygen atoms in the polyatomic ion, so the oxygen atoms contribute -6 to the valency of the polyatomic ion. The one carbon atom has a valency of 4+. The overall charge on the carbonate ion is -6 +4 = -2. So carbonate has a charge of -2.