Writing Formulas for Ternary Ionic Compounds
What is the ratio of the ions in aluminum nitrate?
What is the formula for aluminum nitrate?
1. Read and Understand
What information are you given?
The name of the compound is aluminum nitrate.
2. Plan and Solve
List the symbols and charges for the cation and anion.
Al ion has a charge of 3+ and NO3 ion has a charge of 1_.
Determine the ratio of ions in the compound.
Al with a 3+ charge needs three NO3 ions, each with a charge of 1_.
The ratio of the ions in the compound is 1 to 3.
Because you need more than one polyatomic ion, parentheses must be used.
Write the formula for aluminum nitrate.
Al(NO3)3
3. Look Back and Check
Is your answer reasonable?
Each aluminum atom loses three electrons and each nitrate atom gains one electron. So there
should be a 1 to 3 ratio of aluminum ions to nitrate ions.
Practice
What is the formula for…
magnesium acetate
potassium hydroxide
calcium sulfate
lithium phosphate
tin (II) carbonate
tin (IV) hydroxide
strontium nitrate
lead (II) acetate
gallium sulfate
lead (IV) carbonate
ammonium carbide
aluminum phosphate
ammonium iodide