Writing Formulas for Binary Ionic Compounds

Writing Formulas for Binary Ionic Compounds

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

Metal + Non-Metal = Ionic Compound

If we only have two different types of elements in an ionic compound it is Binary Ionic.

• Potassium bromide
• Calcium chloride
• Aluminum nitride

Practice: The key to success.

Keys for Writing Formulas for Binary Ionic Compounds:

• Write the symbols for each element.
• Find the charge for each element using the Periodic Table. Write it above each element.
• 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 as CaS.