In this video we'll write the correct formula for Zinc phosphide (Zn3P2). To write the formula for Zinc phosphide we’ll use the Periodic Table and follow some simple rules.

Keys for Writing Formulas for Binary Ionic Compounds:

1. Write the symbols for each element.
2. Find the charge for each element using the Periodic Table. Write it above each element. For help finding charge, watch: https://youtu.be/N4N1Njh7nCo .
3. See if the charges are balanced (if they are you're done!)
4. Add subscripts (if necessary) so the charge for the entire compound is zero.
5. Use the crisscross method to check your work.

Notes:
- Don’t write the subscript '1'.
- If you use the criss-cross method and end up with something like Ca2S2 you'll need to reduce the subscripts to Ca1S1 which we write as CaS.

For a complete tutorial on naming and formula writing for compounds, like Zinc phosphide and more, visit:

http://www.breslyn.org/chemistry/naming

Drawing/writing done in InkScape. Screen capture done with Camtasia Studio 4.0. Done on a Dell Dimension laptop computer with a Wacom digital tablet (Bamboo).