1. Naming Compounds and Writing Formulas for Ionic Compounds
Chapter 9 Section 2

2. Naming Binary Ionic Compounds
Composed of two elements
Cation name followed by anion name
NaF
CaCl2
Li3N
Sodium fluoride
Calcium chloride
Lithium nitride

3. Naming Binary ionic compounds with transition metals
Recall transition metal ions have multiple charges
First start with ion that only has one possible charge
“position of strength”
Then determine transition metal ionic charge.
Example: CuO
Copper and oxygen
Copper can be +1 or +2…
…but Oxygen is always -2. Position of strength!
1:1 ratio means this copper must be +2 to cancel out the -2 of the oxygen atom.
Copper (II) oxide

4. You try it! SnS2 FeCl3 SnF2 CuI2 CoI2 CuI Tin (IV) sulfide
Iron (III) chloride
Tin (II) fluoride
Copper (II) iodide
Cobalt (II) iodide
Copper (I) iodide

5. Writing Formulas for Binary Ionic Compounds
Write the symbol for the cation followed by the symbol for the anion.
Add whatever subscripts are needed to balance the charges.
Potassium chloride
Calcium bromide

6. A little trickier… Iron (III) oxide How do you balance this?
Iron (III) is Fe3+
Oxide is O2-
How do you balance this?
Crisscross method, or finding the least common multiple method.

7. Iron (III) Oxide (Rust)
LCM Method
3x2 = 6 (least common multiple)
Two Fe3+ cations have a net charge of: +6
Three O2- anions have a net charge of: -6
Balanced formula for Iron(III) Oxide is Fe2 O3

8. Crisscross Method
Numerical charge of each ion is crossed over and used as a subscript for the other ion
The signs of the numbers are dropped.
Fe3+ O2-
Fe2O3
2(3+) + 3(2-) = 0

9. Crisscross doesn’t always work…
Calcium Sulfide
Ca S2-
Ca2 S2
Remember: formulas for ionic compounds show the lowest whole-number ratios of ions
The correct formula for Calcium sulfide is CaS
1(2+) + 1(2-) = 0
Crisscross method unnecessary in this case

10. Ternary Ionic Compounds
Ternary Compound: A compound that contains atoms of 3 different elements
Most ternary ionic compounds contain a polyatomic ion
THIS IS WHY YOU NEED TO HAVE THEM MEMORIZED!!! You need to recognize polyatomic ions quickly

11. Example: write the formula from the name
How would you write the formula for calcium nitrate?
Write the formula (symbol and charge) for each ion
Balance the charges (hint: use crisscross here)
Ca2+ and NO3-
Ca(NO3 )2
Include parenthesis around the polyatomic ion followed by the subscript of how many of those ions are needed to balance the charge of the compound

12. More examples
If you only need one of the polyatomic ions to balance the charge of the compound, you do not need to use parentheses
Calcium Carbonate
Ca2+ and CO32-
CaCO3
No parentheses
Strontium Sulfate
Sr2+ and SO42-
SrSO4
Lithium Carbonate
Li+ and CO32-
Li2 CO3

13. Write the formulas for the following
Potassium Sulfate
K+ and SO42-
K2 SO4
Magnesium Hydroxide
Mg2+ and OH-
Mg(OH)2

14. Naming Ternary Ionic Compounds
Name the cation first, followed by the anion
Determine the charge of the polyatomic ion.
Balance the polyatomic anion by adding an appropriate subscript for the cation.
K2Cr2O7
Composed of K+ and Cr2O7-2
potassium dichromate

15. Name the following Compounds
LiCN
Lithium Cyanide
Sr(H2PO4 )2
Strontium dihydrogen phosphate
(NH4 )2 C2O4
Ammonium Oxalate
Fe(ClO3)3
Iron (III) Chlorate