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Example 2.8: Composition of Ions

An ion found in some compounds used as antiperspirants contains 13 protons and 10 electrons. What is its symbol?

Solution

\(N_{\mathrm{\ce{p+}}}\) \(= 13\)


\(N_{\mathrm{\ce{e-}}}\) \(= 10\)


Because the number of protons remains unchanged when an atom forms an ion, the atomic number of the element must be 13. Knowing this lets us use the periodic table to identify the element as Al (aluminum). The Al atom has lost three electrons and thus has three more positive charges (13) than it has electrons (10).

\(N_{\mathrm{charge}}\) \(= N_{\mathrm{\ce{p+}}} - N_{\mathrm{\ce{e-}}}\)

\(\ \ \ =13 - 10\)

\(\ \ \ =3\)


This is the aluminum cation, \(\ce{Al^3+}\).