1. Here is the example in video form.

2. We’re asked to write the formula for calcium carbonate Write the formula for calcium carbonate Ca 2+ CO 3 2– +2 –2 Total Positive Charge Total Negative Charge

3. We start by finding calcium on the periodic table. Write the formula for calcium carbonate Ca 2+ CO 3 2– +2 –2 Total Positive Charge Total Negative Charge

4. It’s ion has only one possible charge, positive 2. (click) So its just Ca 2 plus Write the formula for calcium carbonate Ca 2+ CO 3 2– +2 –2 Total Positive Charge Total Negative Charge

5. The second word carbonate, ends in “Ate”, Write the formula for calcium carbonate Ca 2+ CO 3 2– +2 –2 Total Positive Charge Total Negative Charge

6. so it must be a polyatomic ion Write the formula for calcium carbonate Ca 2+ CO 3 2– +2 –2 Total Positive Charge Total Negative Charge It must be a polyatomic ion

7. Looking on the ion table, we see that carbonate is CO3 with a negative 2 charge. Formulas and Charges of Common Ions calcium carbonate

8. So we’ll write CO3 2 minus here Write the formula for calcium carbonate Ca 2+ CO 3 2– +2 –2 Total Positive Charge Total Negative Charge

9. With one calcium ion and one carbonate ion, (click) The total positive charge is positive two Write the formula for calcium carbonate Ca 2+ CO 3 2– +2 –2 Total Positive Charge

10. And the total negative charge is negative 2 Write the formula for calcium carbonate Ca 2+ CO 3 2– +2 –2 Total Positive Charge Total Negative Charge

11. These add up to zero, so they are balanced. Write the formula for calcium carbonate Ca 2+ CO 3 2– +2 –2 Total Positive Charge Total Negative Charge These add up to zero

12. So the formula is just CaCO3. Write the formula for calcium carbonate Ca 2+ CO 3 2– Formula: CaCO 3

13. Because there is only one carbonate ion in the formula Write the formula for calcium carbonate Ca 2+ CO 3 2– Formula: CaCO 3 Only 1 carbonate ion in the formula, so no brackets!

14. No brackets are needed around the CO3 in the formula. Write the formula for calcium carbonate Ca 2+ CO 3 2– Formula: CaCO 3 Only 1 carbonate ion in the formula, so no brackets!

15. So the final answer is: The formula for calcium carbonate is (Click) CaCO3 Write the formula for calcium carbonate Ca 2+ CO 3 2– Formula: CaCO 3