How to Write the Formula for Potassium iodate

Published: 08 May 2021
on channel: Wayne Breslyn (Dr. B.)

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In this video we'll write the correct formula for Potassium iodate (KIO3).

To write the formula for Potassium iodate we’ll use the Periodic Table, a Common Ion Table, and follow some simple rules.

Because Potassium iodate has 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 element symbol for the metal and its charge using Periodic Table.
2. Find the name and charge of the polyatomic ion on the Common Ion Table (see    • Figuring out the Charge on Ions  ).
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.

--Formula Writing Resources--

Finding Ionic Charge:    • Figuring out the Charge on Ions
Memorizing Polyatomic Ions:    • Memorizing and Using the List of Poly...
Criss-Cross Method:    • The Criss-Cross Method for Writing Ch...
For a complete tutorial on naming and formula writing for compounds, like Potassium iodate and more, visit:

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

Drawing/writing done in InkScape (http://www.InkScape.org). Screen capture done with Camtasia Studio 8.0

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