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Polyatomic Ions

Polyatomic Ions

Introduction: All around us are polyatomic ions, or charged chemical species made up of two or more atoms bonded that can be considered to be acting as a single unit. Examples of polyatomic ions that exist around us are bicarbonate ions (found in baking soda), acetate ions (found in nail polish), nitrate ions (found in some hot dogs), perchlorate ions (found in fireworks), carbonate ions (found in glass), peroxide ions (found in mouthwash), and phosphate ions (found in dairy).

Because polyatomic ions consist of many atoms combined together to form the ion, the total charges of the oxidation states in the ion itself is equal to the charge on the ion. This makes up the difference between polyatomic ions and compounds, since compounds are neutral, having a total oxidation state of zero. Polyatomic ions are named accordingly, based on the number of oxygen atoms and the specific types of ions that are involved in the ions.

One group of polyatomic ions are oxyanions, or negatively-charged ions that form when nonmetals combine with oxygen. Elements that commonly form oxyanions include boron, carbon, nitrogen, phosphorus, sulfur, chlorine, arsenic, selenium, bromine, and iodine. In general, phosphate, arsenate, sulfate, and selenate ions are ions that involve a nonmetal combining with four oxygen atoms. The other oxyanions that have an -ate ending have three oxygen atoms. There are also ions, whose endings change, based on the number of oxygen ions.

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