1. Counting Atoms in Formulas Practice

2. 3H2O The coefficient tells you the number of molecules.
H2O H2O H2O
The subscript tells you how many atoms of that element in each molecule.

3. 2H2O 1
Add your 1s 2
Molecules =
H =
O =
Total = 4 2 6

4. H2O 1 1
Add your 1s 1
Molecules =
H =
O =
Total = 2 1 3

5. 4CO2
Add your 1s 1 4
Molecules =
C =
O =
Total = 4 8 12

6. H2O2 1 1
Molecule =
H =
O =
Total = 2 2 4

7. C6H12O6 1 1
Molecule =
C =
H =
O =
Total = 6 12 6 24

8. NH3 1 1 1
Molecule =
N =
H =
Total = 1 3 4

9. 2N2 2
Molecules =
N =
Total = 4 4

10. CH4 1 1 1
Molecules =
C =
H =
Total = 1 4 5

11. 2HCl 1 1 2
Molecule =
H =
Cl =
Total = 2 2 4

12. 3CaCO3 1 1 3
Molecules =
Ca =
C =
O =
Total = 3 3 9 15