COUNT ATOM How to count atoms

2H2O COEFFICIENT SUBSCRIPT

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

2H2O 2MOLECULES!!!!

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.

2H2O 4 2 How many hydrogen atoms are present? 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: 4CaCO3

4CaCO3 Ca -1 x 4 = 4 C – 1 x 4 = 4 O – 4 x 3 = 12 This molecule has 4-Ca, 4-C, and 12-O. The total number of atoms present is 12 + 4 + 4 = 20

3CO2

3CO2 C – 3 x 1 = 3 O – 3 x 2 = 6 There are 3 – C, 6 – O. The total number of atoms is 6 + 3 = 9

2C6H12O6 GLUCOSE

2C6H12O6 C – 2 x 6 = 12 H – 2 x 12 = 24 O – 2 x 6 = 12 The total number of atoms is 48

6K2SO4

6K2SO4 K – 6 x 2 = 12 S – 6 x 1 = 6 S – 6 x 1 – 6 O – 6 x 4 = 24 Total number of atoms 48

CaMg(CO3)2

CaMg(CO3)2 Ca – 1 Mg – 1 C – 1 x 2 = 2 O - 3 x 2 = 6 Total number of atoms is 10

3Pb(NO3)2 Pb – 3 x 1 = 3 N – 3 x 1 x 2 = 6 O – 3 x 3 x 2 = 18 Total number of atoms 27