1. Ionic Compounds: Writing Type 1 Formulas

2. PolyAtomic Ions
A molecule that is made up of 2 or more atoms that act as a unit and have an overall charge.
Since the polyatomic ion acts as a unit, we treat them like we would a single element.
How to recognize if the compound has a polyatomic ion:
Count how many elements there are in the compound.
If there are more than 2-you have a polyatomic ion and you can find it in the chart.

3. Writing Ionic (Type I) Formulas Using the Criss-Cross Method
Steps:
Write the cation (+) first followed by the anion (-).
Mg Cl
Determine the charges using the periodic table and write them as superscripts.
Mg Cl-
Remember: the positive must equal negative! Drop the positive or negative sign and criss-cross the numbers to become new subscripts.
Mg2 Cl1
Write the new formula with no charges and subscripts.
MgCl2
Reduce when possible.

4. Examples: Colored Card Shuffle
K and O
Al and F
Be and N
Mg and S