1. Polyatomic Ionic Compounds

2. Polyatomic Ions
Polyatomic Ions consist of one or more nonmetal atoms that form covalent bonds, but are not stable – they carry a charge.
There is only 1 common polyatomic Cation and it is ammonium: NH4+
Most polyatomic ions are Anions:
SO42- Sulfate NO Nitrate

3. Names
Names of polyatomic ions that contain oxygen will end in -ate or -ite
-ite is one less oxygen than ate
Example
Sulfate is SO42- Sulfite is SO32-
Chlorate is ClO31- Chlorite is ClO21-

4. Writing Formulas The polyatomic ion is treated as one unit.
Use the crossover method – remember you are only crossing the charge’s number only!!
Place parenthesis around the polyatomic ion if there is more than one
Example
Write the formula for Iron (II) Nitrate
Fe2+ and NO3-
Fe(NO3)2

5. Ammonium Sulfide
NH S2-
(NH4) 2 S

6. Practice Sodium Phosphite Barium Imide Hydrogen Peroxide
Calcium Iodate
Copper (II) Sulfate
Na3 PO3
BaNH
H2 O2
Ca(IO3)2
CuSO4

7. Naming
Name the metal then name the polyatomic ion. If you need a roman numeral, include it.
Treat the polyatomic ion as one unit (as if it were one atom)
Example - Name CaSO4
Calcium Sulfate

8. Let’s Try Na3 PO3 Na is Sodium PO3 is Phosphite
So…… Sodium Phosphite!!!

9. What if I have a Multivalent Ion with a Polyatomic Ion???
It’s ok! You already know what to do!!!
Example - Name CuSO4
I know right away that SO4 is Sulfate and that Cu is Copper – but what level of Copper. So I need to follow the steps I learned Thursday!
Find the charge number for SO4 and it is 2-
Then I multiply the charge number by how many SO4 I have – which is 1 : 2x1=2
And then I divide that number by how many Cu I have – which is 1 : 2/1=2
Which means the Roman Numeral is II
Copper (II) Sulfate

10. Practice! KCN Na3AsO3 Al2(S2)3 BaC2O4 Fe3 (BO3)2 Potassium Cyanide
Sodium Arsenite
Aluminum Disulfide
Barium Oxalate
Iron (II) Borate