1. Ionic Bonding:
Polyatomic Ions & Roman Numerals

2. Ex: (NO3)1- Polyatomic Ions Ionic compounds with polyatomic ions
– Polyatomic Ion – a charged group of covalently bonded
atoms that stay bonded together during chemical reactions
Ex: (NO3)1-

3. Polyatomic Ions The STAAR Chart contains the most
common Polyatomic Ions
You have the list – Keep it!
Also, these are not ALL the polyatomic ions that exist, but the ones you will see in this course.

4. Writing Formulas with Polyatomic Ions
Example #1: Ammonium chloride
NH4Cl
NH4 Cl
+1 1–
Example #2: Copper (II) sulfate
CuSO
Cu+2
SO4 2– 4
NEVER drop the polyatomic ion’s original subscripts!!

5. Writing Formulas with Polyatomic Ions
When more than one of a particular polyatomic ion is present,
parentheses are needed
Parentheses go around the entire formula of the polyatomic ion with the NEW subscript outside parentheses
– Subscript describes the number of polyatomic ions
Example #3: Ammonium carbonate
NH4
(NH4)2CO3 +1
CO3 2–

6. NH +1 SO 2– Sr+2 OH1– Ba+2 Fe+3 More Examples Ammonium sulfate
4 4
Strontium hydroxide
Sr+2 OH1–
Barium phosphate
• (NH4)2SO4
Sr(OH)2
• Ba3(PO4)2
Ba+2
PO4 3–
Iron (III) nitrite
Fe(NO2)3
Fe+3
NO2 1–

7. Naming Ionic Compounds with Polyatomic Ions
Ionic compound naming pattern
NEVER change a polyatomic ion’s name.
cation’s name + anion’s name
Ex) NH4NO3 = ammonium nitrate
Don’t forget to check if the CATION is a Transition Metal. If so, a
Roman Numeral is required.

8. Examples Mg(OH)2 Magnesium hydroxide • (NH4)2S Ammonium sulfide Cu2SO4
FeSO3
NH4OH
Magnesium hydroxide
Ammonium sulfide
Copper (I) sulfate
Iron (II) sulfite
Ammonium hydroxide

9. 1
Sodium phosphate

10. 2
Calcium carbonate

11. 3
Potassium chloride

12. Sodium hypochlorite 4

13. 5
Ammonium hydrogen carbonate

14. Writing Ionic Formulas with Roman Numerals
Write ions with charges
-The Transition metal’s charge IS the Roman numeral
- Anions & Polyatomics have fixed charges so use the periodic table
Cross and drop charges
Reduce subscripts to the
lowest whole number ratio
Ex) Write the formula for lead(IV) oxide.
Step 1 & 2: Pb4+ O–2
Step 3: Pb2O4
Step 4: PbO2
The charges of the ions balance each other so the overall charge is zero.
Oxidation state will be written in the name as a Roman numeral
Roman numerals 1-10 = I, II, III, IV, V, VI, VII, VIII, IX, X

15. Cu2+ S-2 Cu1+ S-2 Fe2+ N-3 Fe3+ Cl-1 More Examples Copper (II) sulfide
Copper (I) sulfide
Cu1+ S-2
Iron (II) nitride
Fe2+ N-3
Iron (III) chloride
Fe3+ Cl-1
Cu2S2 = CuS
Cu2S
Fe3N2
FeCl3

16. Naming Compounds with Roman Numerals
Some metals have more than one oxidation state
– In these cases, Roman numerals are used to denote the charge of the ion in the compound
Binary ionic compound containing multiple oxidation state metal naming pattern
metal’s name(Roman numeral) + non-metal’s stem + -ide
= iron (II) fluoride
Ex) FeF2

17. Fixed & Multiple Charged Metals
In the table below
– Metallic cations with a fixed charge
– Common oxidation states of metals that form more than one cation

18. Metals with FIXED charges
►Metals with fixed charges will NOT have roman numerals next
to their names.
►MEMORIZE the following elements AND their charges.
Group 1 (1A) = +1
Group 2 (2A) = +2
Group 13 (3A) = +3
Group 14 (4A) = +4 (do not participate in Ionic bonds)
Group 15 (5A) = –3
Group 16 (6A) = –2
Group 17 (7A) = –1
►Zinc (Zn) = +2
►Silver (Ag) = +1
►Cadmium (Cd) = +2

19. Metals with MULTIPLE charges
Only metals with multiple charges have a roman numeral in the
name of the compound.
The following metals WILL have roman numerals as a
part of their name.
All metals in groups 3-12
EXCEPT zinc (Zn), silver (Ag), and cadmium (Cd)
Tin (Sn) = +2 or +4
Lead (Pb) = +2 or +4
Indium (In) = +1 or +3
Thallium (Tl) = +1 or +3

20. Naming Ionic Compounds with Roman Numerals
 Example #1: What is the name of FeF2?
 Finding the Roman Numeral for metals with Multiple Charges:
Multiply the anion’s charge by the anion’s subscript.
Then, drop the negative sign & divide by the cation’s subscript.
That will give you the roman numeral.
 Example Continued:
FeF2 : First, –1 x 2 = –2
Iron’s oxidation number = +2
NAME OF FeF2 = Iron (II) fluoride
Then, 2/1 = 2

21. Naming Ionic Compounds with Roman Numerals
Example #2: What is the name for CuO?
• CuO : First, –2 x 1 = –2
Then, 2/1 = 2
Copper’s oxidation number = +2
NAME OF CuO = Copper (II) oxide

22. More Examples Iron (III) chloride FeCl3 Cu3P PbO Copper (I) phosphide
Zn3N2
MnO2
Copper (I) phosphide
Lead (II) oxide
Zinc nitride
Manganese (IV) oxide