Practice!

Sample Problem

How many atoms are in the compound Ca(NO3)2?

Solution

This compound is composed of the elements calcium, nitrogen, and oxygen. Subscripts indicate the number of the element or compound they are associated with. In this case, the 3 under oxygen shows that there are 3 oxygen atoms, therefore NO3 consists of 4 atoms. The subscript 2 around the parenthesis shows that there are two NO3 in the overall compound, doubling the amount of atoms to 8, plus the calcium atom to get the solution 9.