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 ION
Example 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 unknown
Six 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 Problems
Write the correct formulas for each compound
• Sodium nitrate
• Calcium chlorate
• Aluminum carbonate
• Potassium sulfate
Practice Problems
Write 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 Problems
Name the following compounds.
• KOH
• Cu(NO3)2
• AlPO4
Practice Problems
Name the following compounds
• NaC2H3O2
• NaCN
• PbSO4