## Chemistry: Principles and Practice (3rd Edition)

(a) I$^{1-}$ (b) Mg$^{2+}$ (c) O$^{2-}$ (d) Na$^{1+}$
(a) I$^{1-}$ The elemental symbol for iodine is I. Iodine is in group 17; therefore, it has a valence of 1-. (b) Mg$^{2+}$ The elemental symbol for magnesium is Mg. Magnesium is in group 2; therefore, it has a valence of 2+. (c) O$^{2-}$ The elemental symbol for oxygen is O. Oxygen is in group 16; therefore, it has a valence of 2-. (d) Na$^{1+}$ The elemental symbol for sodium is Na. Sodium is in group 1; therefore, it has a valence of 1+.