In this video we'll write the correct formula for Chromium (III) iodide (CrI3).

To write the formula for Chromium (III) iodide we’ll use the Periodic Table and follow some simple rules.

---Keys for Writing Formulas for Compounds with Transition Metals---
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 (see [ Ссылка ]).
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.
- 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.

---Formula Writing Resources---
Finding Ionic Charge: [ Ссылка ]
Memorizing Polyatomic Ions: [ Ссылка ]
Criss-Cross Method: [ Ссылка ]

For a complete tutorial on naming and formula writing for compounds, like Chromium (III) iodide and more, visit:

[ Ссылка ]

Drawing/writing done in InkScape. Screen capture done with Camtasia Studio 8.0

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