1. Criss-Cross Method: Writing Ionic Formula
Step 1
Symbol for cation (left) then anion (right)
Potassium oxide: K O
Step 2
Write cation charge
K1+ O
group 1: loses 1 electron
Step 3
write anion charge
K1+ O2-
group 16: gain 2 electrons
Step 4
Check to see if charge = 0
if they don’t crisscross:
cation superscript  anion subscript
anion superscript  cation subscript
K1+ O2- = 1-  0 
K1+ O 2- => K2O
Step 5
REDUCE if you can
Can’t be reduced

2. Practice
Gallium Oxide
2. Magnesium Phosphate
3. Titanium (IV) Sulfate

3. 4. Rubidum Phosphide 5. Lead (IV) Iodide 6. Ammonium Oxide