COUNT ATOM How to count atoms 2 H

COUNT ATOM How to count atoms

2 H 2 O COEFFICIENT SUBSCRIPT

2 H 2 O 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

2 H 2 O 2 MOLECULES!!!!

2 H 2 O 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.

2 H 2 O How many hydrogen atoms are present? 4 How many oxygen atoms are present? 2

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

Let’s try an example: 4 Ca. CO 3

4 Ca. CO 3

1. Write down symbols Ca C O 4 Ca. CO 3

Write down the coefficient next to each symbol Ca 4 C 4 O 4 4 Ca. CO 3

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

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

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

3 CO 2

3 CO 2

2 C 6 H 12 O 6 GLUCOSE

2 C 6 H 12 O 6

6 K 2 SO 4

6 K 2 SO 4

Ca. Mg(CO 3)2

Ca. Mg(CO 3)2

3 Pb(NO 3)2

3 Pb(NO 3)2