Writing Formulas for Ternary Ionic Compounds

Ternary Ionic Compounds: Formula Writing

When we have a metal and a non-metal we have an ionic compound.

Metal + Non-Metal = Ionic Compound

If we have a metal and a polyatomic ion we have a ternary ionic compound.

• Sodium nitrate
• Calcium carbonate
• Aluminum hydroxide

Practice: The key to success.

Keys for Writing Formulas for Ternary Ionic Compounds:

• Write the element symbol for the metal and its charge using Periodic Table.
• Find the name and charge of the polyatomic ion on the Common Ion Table.
• See if the charges are balanced (if they are you're done!)
• Add subscripts (if necessary) so the charge for the entire compound is zero.
• 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.