Monovalent ions: +1 = Group 1 (H, Li, Na, K, Ag), +2 = Group 2 (Be, Mg, Ca, Sr, Ba, Zn, Cd), -2 = Group 6A (Oxide, Sulfide), -1 = Group 7A (Fluoride, Chloride, Bromide, Iodide)
Multivalent ions: +1, +2 = Hg, Cu, +1, +3 = Au, +2, +3 = Fe, Co, Ni, +3, +5 = Bi, Sb