Answer
(a) Li$^{+}$
(b) S$^{2-}$
(c) I$^{-}$
(d) N$^{3-}$
(e) Al$^{3+}$
(f) Cs$^{+}$
(g) Mg$^{2+}$
Work Step by Step
(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$^{2+}$.
