COUNT ATOM How to count atoms

2H2O COEFFICIENT SUBSCRIPT

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.

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

1. Write down symbols 4CaCO3 Ca C O

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

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

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

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

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