1. COUNT ATOM
How to count atoms

2. 2H2O
COEFFICIENT
SUBSCRIPT

3. Words to know
Coefficients are whole numbers written to the left of a formula.
Subscripts are written to the right of an element. It tells you how many units of that element you have.

4. The coefficient gets applied to the ENTIRE formula
2H2O
The coefficient gets applied to the ENTIRE formula
-this means that there are 2 molecules of water present!
-you MULTIPLY this number by every subscript in the formula

5. 2H2O
2MOLECULES!!!!

6. The subscript only gets applied to the element it follows
2H2O
The subscript only gets applied to the element it follows
-If there is no subscript present, it is assumed that there is only 1 atom of that element in the molecule.

7. 2H2O 4 2 How many hydrogen atoms are present?
How many oxygen atoms are present? 2

8. The easiest way to count atoms:
1. Write down all of the symbols for all of the elements present in the formula
2. If there is a coefficient, write this number next to each of the symbols
3. Multiply the coefficient by the subscripts of each of the elements present in the formula

9. Let’s try an example:
4CaCO3

10. 4CaCO3

11. 1. Write down symbols
4CaCO3 Ca C O

12. Write down the coefficient next to each symbol
4CaCO3 Ca C O 4

13. Multiply by the subscript
4CaCO3 Ca C O 4 X 1 3

14. Multiply…
4CaCO3 Ca C O 4 X 1 3 = 4 12

15. Add totals together to get the total amount of atoms
4CaCO3 Ca C O 4 X 1 3 = 4 12
20 atoms

16. Complete the following Using your steps
NaOH
4HNO3
MgCl2
2NaOH
4Li2O