Polyatomic Ions Writing Formulas / Naming Compounds A polyatomic ion is a covalent molecule that has an ionic charge. (As opposed to being a neutral molecule.) Poly = many Atomic = atoms Ion = charged particle A charged particle that consists of more than one atom.

Polyatomic Ions Examples: Sulfate = SO4-2 Nitrate = NO3-1 Phosphate = PO4-3 Chlorate = ClO3-1 Carbonate CO3-2 Notice the ending has changed to –ate.

Writing Formulas Sodium Phosphate Write the formula for the metal. Add the oxidation number from the periodic table. Na+1 Write the formula for the polyatomic ion from the ion chart. Add its oxidation number. PO4-3

Sodium Phosphate Na +1 PO4-3 “Swap and drop” the charges to make them the subscripts. When possible, divide by the greatest common factor to simplify the subscripts. Na3PO4

Calcium Phosphate Write the formula for the metal. Add the oxidation number from the periodic table. Ca+2 Write the formula for the polyatomic ion from the ion chart. Add its oxidation number. PO4-3

Calcium Phosphate Ca +2 PO4 -3 “Swap and drop” the charges to make them the subscripts. When possible, divide by the greatest common factor to simplify the subscripts. Ca3(PO4)2 Notice that the polyatomic ion must be placed in parenthesis or, instead of 2 phosphate ions, you would have 42 Oxygen atoms and 1 Phosphorus atom. Ca3PO42

Now you try!

Naming Compounds w/ Polyatomic Ions KClO3 Write the name of the metal. Potassium Write the name of the polyatomic ion from the ion chart. Chlorate Name the compound. Potassium Chlorate

Mg3(SO4)2 Name the metal. Name the polyatomic ion from the ion chart. Magnesium Name the polyatomic ion from the ion chart. Sulfate Name the compound. Magnesium Sulfate

Try these Write names for the following compounds. CaCO3 Al2(SO4)3 Ca(ClO3)2 K3PO4 Mg(OH)2

Answers Calcium carbonate Aluminum sulfate Calcium chlorate Potassium phosphate Magnesium hydroxide

Now, these! Write formulas for the following compounds. Lithium sulfate Calcium carbonate Aluminum nitrate Magnesium phosphate Sodium hydroxide

Answers Li2SO4 Ca(C2H3O2)2 Al(NO3)3 Mg3(PO4)2 Na2CO3