Ternary Compounds

• Ternary Compound – an ionic compound that contains more than two different elements

• Polyatomic ion – an ion that is made up of more than one atom

• The charge given to a polyatomic ion applies to the entire group of atoms. The polyatomic ion acts as an individual ion.

• Examples of polyatomic ions:

Sulfate SO4-2

Phosphate PO4-3

Hydroxide OH-

Because a polyatomic ion exists as a unit, never change the subscripts of the atoms within the ion. If more than one polyatomic ion is needed, place parentheses around the ion and write the appropriate subscript outside the parentheses.

Writing the Formula for an Ionic Compound containing a

POLYATOMIC IONExample 1: Write the formula for calcium phosphate.

Step 1: Analyze the Problem.First write each ion along with its charge

Ca+2 PO4-3

Step 2: Solve for the unknownSix is the smallest number evenly divided by

both ionic charges. Therefore a total of six electrons were transferred. The amount of the negative charge of two phosphate ions equals the amount of positive charge of three calcium ions.

Ca+2 ( PO4)-3

“cross charges”

Ca+2 (PO4)-3

• To use a subscript to indicate more than one unit of a polyatomic ion, you must place the polyatomic ion in parentheses and add the subscript to the outside. The correct formula is :

Ca3(PO4)2

Practice ProblemsWrite the correct formulas for each compound

• Sodium nitrate

• Calcium chlorate

• Aluminum carbonate

• Potassium sulfate

Practice ProblemsWrite the correct formulas for each compound

• Magnesium phosphate

• Iron (III) nitrate

• Copper (I) hydroxide

• Sodium acetate

Naming Compounds that contain Polyatomic Ions

• Naming compounds that contain polyatomic ions is really no different than naming other ionic compounds except that the ending of the name does NOT change.

Name of cation + Name of Polyatomic Ion

• Remember, if the 1st element is a TRANSITION METAL

or a metal with MORE THAN 1 CHARGE

USE ROMAN NUMERALS

Practice ProblemsName the following compounds.

• KOH

• Cu(NO3)2

• AlPO4

Practice ProblemsName the following compounds

• NaC2H3O2

• NaCN

• PbSO4