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Polyatomic Ions

You need to memorize the following information. a You should be able to write the formula (including the charge, which is the superscript) of all of the following polyatomic ions, if given the name. o When there are two of the same kind of polyatomic ions in a formula, the polyatomic ion is put in parentheses and the subscript outside of the parentheses tells you how many polyatomic ions there are. o There is one hydroxide ion in NaOH and there are two hydroxide ions in Ca(OH)2. a You should also be able to write the name of any of the polyatomic ions, if the formula is given (the formula will include the charge, if the polyatomic ion is alone. The charge is NOT included in the formula of a compound because the entire compound is neutral. a You also need to memorize the formulas of the molecules below that are ionic compounds because they contain polyatomic IONS, and a learn the common uses for these substances. Be able to write the formula if asked, for example, what is the chemical formula for bleach? a Finally, learn the names of the following IONIC molecules. They will help you remember the naming rules for IONIC compounds.

Chemical Formula



ammonium perchlorate

This pollutant is being cleaned up (don't panic!) , but it has also been found recently (2007) in lettuce because the untreated water from the Colorado River is used to irrigate farmland. It can cause cancer and damage the thyroid. sodium hypochlorite NaClO

Reason for Knowing this formula This is a common pollutant in our drinking water! The source is the Colorado River. The substance leached into the river from a factory that made ammonium perchlorate as a component of rocket fuel. This is usually the formula for a "chlorine bleach" used in liquid bleaches.

Polyatomic Ions Formula NH4+ and ClO4-

Name of polyatomic Ion ammonium and perchlorate




Polyatomic Ions

Chemical Formula Name calcium carbonate Reason for Knowing this formula This is the main component of sea-shells, and chalk. Also it is the antacid in TUMS, and the white, chalky looking substance on the surface of concrete. Baking soda! This can neutralize either an acid or a base and make it harmless through a chemical reaction. A fertilizer that adds nitrogen to the soil, (nitrogen is an important plant nutrient) and an explosive! This is one kind of rust. Turquoise rocks (the kind in jewelry) Phosphates are also used in detergents, fertilizers. Hydroxides are bases (opposite of an acid). Polyatomic Ions Formula CO32Name of polyatomic Ion carbonate



sodium hydrogen carbonate


hydrogen carbonate (also called bicarbonate)


ammonium nitrate

NH4+ NO3-

ammonium nitrate


(You don't have to memorize this formula!!)

iron (III) oxide I don't even know the proper chemistry!



Contains PO43and OHhydroxide phosphate

CuAl6(PO4)4(OH)8·5H2O Rocks and gems often have complicated formulas like this one.


Polyatomic Ions

Chemical Formula Name Reason for Knowing this formula Polyatomic Ions Formula Name of polyatomic Ion sulfate


magnesium sulfate

(actually Epsom salts are MgSO4(H2O)7, but don't (magnesium worry about that for this sulfate heptahydrate) exercise.) NaCN Or KCN potassium cyanide sodium cyanide

SO42Epsom salts, also used to treat magnesium deficiencies in soil When ingested, NaCN or KCN chemically reacts to form HCN (hydrogen cyanide) which is a poison. HCN gas has also been used to kill people in large groups. It was the gas in the gas chambers used in the Holocaust. This is the "sulfite" labeled on wine. All wine has some sulfite due to the fermentation process. KHSO3 can also be added as a preservative. There is no real evidence that it produces headaches! [it is believed to be a different molecule in wine]. CN-



Potassium hydrogen sulfite or Potassium bisulfite


hydrogen sulfite also called bisulfite



Polyatomic Ions

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