How to Write the Formula for Iron (III) Oxide

In this video we'll write the correct formula for Iron (III) Oxide.

To write the formula for Iron (III) Oxide we’ll use the Periodic Table, a Common Ion Table, and follow some simple rules.

Because Iron (III) Oxidehas a polyatomic ion (the group of non-metals after the metal) we’ll need to use a table of names for common polyatomic ions, in addition to the Periodic Table.

Keys for Writing Formulas for Ternary Ionic Compounds:

1. Write the symbol and charge for the transition metal. The charge is the Roman Numeral in parentheses.
2. Write the symbol and charge for the non-metal. If you have a polyatomic ion, use the Common Ion table to find the formula and charge.
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 CaS.

Note: It is possible to have two polyatomic ions such as NH4NO3. In this case find and write both names as found on the Common Ion Table.

For a complete tutorial on naming and formula writing visit:

thegeoexchange.org/chemistry/naming/resources/l…

or watch

youtu.be/i_bcCmL3U28

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).