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Polyatomic Ions

Definition, naming system and role of charges within compounds

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Where do polyatomic ions exist in everyday life?

A polyatomic ion, or molecular ion, is an ion composed of at least two covalently-bonded atoms. This ion behaves as if it is composed of only a single atom. For example, this large grape is comprised of two grapes but can still represent a single one.

Credit: Kuba Bożanowski
Source: http://www.flickr.com/photos/jbozanowski/3475347571/in/photolist-6i74KH-6w1qBV-6CyKDD-9Fb8Ym-9F8daD-9F8dcX-9Fb99s-ed3ZvV-9GrCBn-8tKWs5-96Ch44-9BKigE-9BKiYm-ao1gyq-83fchj-eddFMF-9aU52F-83fcRQ-dDoSJk-byrTP1-dbrVqT-9F8dcc-7JJLTq-9yTsBX-86R3jz-aE6rTq-aE2ArH-aE2A8c-aE6rNL-aE6rXC-dRp4kj/lightbox/
License: CC BY-NC 3.0

Conjoined grapes [Figure1]

In nature, the polyatomic ions CO2 (carbon dioxide) and SO3 (sulfur trioxide) are significant because the reaction between CO2 and H2O results in global warming while the reaction between SO3 and H2O results in acid rain.

Most common polyatomic ions are negative atoms, other than NH4+ (ammonium). Here are some common polyatomic atoms with the charge of -1 and their uses:

acetate: C2H3O2-  nailpolish
bicarbonate (hydrogen carbonate): HCO3-  baking soda
chlorate: ClO3-  detergents
cyanate: OCN-  paper
cyanide: CN- plastic
hydroxide: OH-  water
nitrate: NO3-  drinking water
perchlorate: ClO4-  fireworks

Here are some common examples of polyatomic ions with the charges -2 and -3 and their uses:

carbonate: CO32- glass
peroxide: O22- mouthwash
sulfite: SO32- wine
borate: BO33-  wood preservatives
phosphate: PO43-  dairy

 Creative Applications

  1. Find and explore the chemical formulas and identities of common polyatomic atoms that you have never before heard of. (use the first resource link if necessary)
  2. Since the charges are usually negative, what is the lowest possible charge of a polyatomic ion?
  3. What does the prefix “poly-” mean and how does it help you understand the meaning of polyatomic?
  4. What are some other polyatomic ions with uses common to everyday life?


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