1. Counting Atoms Obviously, there are more materials in the world than just 100 or so elements on the periodic table.

2. Individual atoms can combine with each other to form a group of atoms called a molecule. Individual atoms can combine with each other to form a group of atoms called a molecule.

3. 1. The symbol of an element represents one atom of that element. Example Na = 1 Sodium atom Na = 1 Sodium atom S = 1 Sulfur atom S = 1 Sulfur atom

4. 2. A subscript is a number written at the lower right corner behind the symbol of an element. If there is more than one atom ‘stuck’ together (in chemistry we call this bonded), a subscript is used to indicate the number of atoms. If there is more than one atom ‘stuck’ together (in chemistry we call this bonded), a subscript is used to indicate the number of atoms.

5. Example) F 2 = two atoms fluorine stuck together H 2 O = 2 atoms of Hydrogen 1 atoms of Oxygen 1 atoms of Oxygen Total # of atoms 3 Total # of atoms 3 C 6 H 12 O 6 = 6 atoms of Carbon 12 atoms of Hydrogen 12 atoms of Hydrogen 6 atoms of Oxygen 6 atoms of Oxygen Total # of atoms 24 Total # of atoms 24

6. 3. A coefficient is a number written in front of a chemical formula. It tells you how many molecules you have. Example) 2 H 2 O = 2 molecules of water 4 total atoms of Hydrogen 4 total atoms of Hydrogen 2 total atoms of Oxygen 2 total atoms of Oxygen