1. Forming New Substances
Chapter 9 - 2
Part 2

2. Writing Formulas - Ionic Compounds
The formula must have subscripts that cause the charges of the ions to cancel out making the compound neutral.
An oxidation number is a positive or negative number.

3. Crisscross Method
1. Write the chemical symbols for each element in the compound (positive 1st)
Ex: compound of calcium & chlorine Ca Cl
2. Write the oxidation numbers above the symbols Ca2+ Cl-
3. Crisscross the oxidation numbers making them subscripts. Ca Cl1-
4. Fill in the formula. CaCl2

5. Continued
If they have the opposite charges or can be reduced, then they cancel each other out.
For example:
Li F = LiF
Al 3+ P = Al3P3 or AlP
Ca C = Ca4C2 or Ca2C
Pb S = Pb2S4 or PbS2

6. Let’s Practice 1. Be N 2. Sr Te 3. Ba Pb 4. K O 5. Mg S 6. Na Cl
Answers:
Be3N2
K2O
Sr2Te2 or SrTe
Mg2S2 or MgS
Ba4Pb2 or Ba2Pb
NaCl

7. NAMING THE FORMULAS
Ionic compounds do not use prefixes like covalent compounds do.
The second name ends in “ide” just like covalent do.
Examples: Be3N2 Beryllium Nitride or CaF2 is Calcium Fluoride

8. WRITING FORMULAS AND NAMING IONIC COMPOUNDS WS
LET’S TRY IT!
WRITING FORMULAS AND NAMING IONIC COMPOUNDS WS