## Chemistry (4th Edition)

(a) Li$^{+}$ (b) S$^{2-}$ (c) I$^{-}$ (d) N$^{3-}$ (e) Al$^{3+}$ (f) Cs$^{+}$ (g) Mg$^{2+}$
(a) Lithium (Li) is in group 1A and has one valence electron. It tends to lose this electron and takes on a +1 charge. The formula of the common ion for lithium is Li$^{+}$. (b) Sulfur (S) is in group 6A and has six valence electrons. It tends to gain two electrons and takes on a -2 charge. The formula of the common ion for sulfur is S$^{2-}$. (c) Iodine (I) is in group 7A and has seven valence electrons. It tends to gain one electron and takes on a -1 charge. The formula of the common ion for iodine is I$^{-}$. (d) Nitrogen (N) is in group 5A and has five valence electrons. It tends to gain three electrons and takes on a -3 charge. The formula of the common ion for nitrogen is N$^{3-}$. (e) Aluminum (Al) is in group 3A and has three valence electrons. It tends to lose these three electrons and takes on a +3 charge. The formula of the common ion for aluminum is Al$^{3+}$. (f) Cesium (Cs) is in group 1A and has one valence electron. It tends to lose this electron and takes on a +1 charge. The formula of the common ion for cesium is Cs$^{+}$. (g) Magnesium (Mg) is in group 2A and has two valence electrons. It tends to lose these two electrons and takes on a +2 charge. The formula of the common ion for magnesium is Mg$^{2+}$.