EXAMPLE  - Predicting Ion Charge:

Predict the charge or charges for the ions formed by atoms of (a) scandium, Sc, (b) gallium, Ga, and (c) sulfur, S. Write an abbreviated electron configuration for each ion and use it to explain why the ion acquires the charge it does.


a. Because scandium is a metal in group 3 on the periodic table, we expect its atoms to lose three electrons each and form +3 cations with the stable 3s23p6 configuration of argon.

       Sc                             Sc3+     +     3e-
[Ar] 3d1 4s2            [Ar] or [Ne] 3s2 3p6

b. Gallium is a metal, so we expect it to form cations. It is in group 13, so we follow the guidelines for cations other than Al3+ and those in groups 1, 2, or 3. The first step is to write the abbreviated electron configuration for an uncharged gallium atom. The noble gas preceding gallium on the periodic table is argon. Gallium atoms can lose one electron to form Ga+ ions with the stable 3d104s2 configuration.

           Ga                           Ga+     +     e-
[Ar] 3d10 4s2 4p1            [Ar] 3d10 4s2

Gallium atoms can also lose three electrons to form Ga3+ ions with the stable 3d10 configuration.

           Ga                          Ga3+     +     3e-
[Ar] 3d10 4s2 4p1               [Ar] 3d10

c. Sulfur is a nonmetal, so we expect its atoms to gain electrons and form anions. Each atom gains two electrons to form a S2- ion with the stable, noble gas electron configuration of argon.

         S      +    2e-       S2-
[Ne] 3s2 3p4                  [Ar]   or  [Ne] 3s2 3p6

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