1. Ionic Compounds Naming/Formula Writing Polyatomic ions
Chapter 4.2
Ionic Compounds
Naming/Formula Writing
Polyatomic ions

2. Polyatomic Ions
A polyatomic ion is a group of atoms, usually of different elements, that together have an overall charge.
Example:
NO3- Nitrate
SO42- Sulfate
PO43- Phosphate

3. NOTICE: They are part of ionic compounds
The name of a polyatomic ion usually has the ending –ate or –ite
Polyatomic ions usually have a negative charge except ammonium which is NH4+
*****see the list of all of polyatomic ions*****

4. Naming Rules 1. Name the metal.
a) If the metal is multivalent, use a roman numeral in brackets after the metal name to indicate the charge of the ion.
b) If NH4 is present write its name ammonia
2. Name the non-metal
a) Write the name of the negative polyatomic ion as it is shown on your list OR
b) Write the name of your non-metal and change the ending to -ide

5. Examples – Name the following compounds
LiOH
Mg3(PO4)2
Al2(SO3)3
NH4S

6. Examples – Naming compounds with multivalent metals and polyatomic ions
Fe2(SO3)3
CuOH
Mn(PO3)3
NiCO3
You must mathematically determine the charge on the metal

7. Writing the formula of an Ionic compound with a polyatomic ion
Rules
Write the symbol of the metal/polyatomic ion with its ion charge as a superscript
Write the symbol of the non-metal/polyatomic ion with its ion charge as a superscript
Criss cross the charges so that they become subscripts for the opposite element and remove + or – signs
Use brackets around polyatomic ions if there is more than one ion after criss crossing
Simplify the subscripts if possible.

8. Example of formula writing
Potassium nitrate
Magnesium sulfate
Ammonium phosphite

9. Examples of formula writing
Copper (II) sulfite
Chromium (VI) hydroxide
Cobalt (III) permanganate

10. Homework
Worksheet
“Polyatomic Ions Naming and Formula Writing”