Polyatomic Ions

• Polyatomic ions are groups of atoms that are bonded and carry a charge.
• The most common polyatomic ions are easily recognized by their suffix -ate / -ite.
• Acids are a special group of polyatomic compounds, formed when hydrogen combines with polyatomic ions containing oxygen, and are some of the strongest acids.
• Examples of polyatomic ions include (NH4)3N, (SO4)2- and (CO3)2-.
• For simple ionic compounds, the number of atoms of each element is indicated by the subscript.
• For polyatomic ions, the same rules apply, but when there is a subscript outside parentheses, that number is applied to each element inside the parentheses.
• An example of this is (NH4)3N, where there are 3 NH4 ions, N x 3 + 1 = 4 N, 4H x 3 = 12 H, 3.
• When writing formulas for polyatomic compounds, the polyatomic ion is treated the same as a single ion.
• When more than one polyatomic ion is needed in the formula, subscripts are used.
• To name polyatomic compounds, first name the metal, then name the polyatomic ion.
• An example of this is K2SO4, where K is the metal and SO42- is the polyatomic ion.