1. How to Count Atoms

2. Symbol The symbol of an element represents one atom of that element.
e.g. Na = 1 atom of Sodium

3. Subscript
A subscript is written behind the symbol of an element in the lower right corner. A subscript is used to indicate the number of atoms if there is more than one atom of the element.
e.g. H2 = 2 hydrogen atoms

4. Subscript outside a bracket
3. A subscript outside a bracket multiples all the elements inside the brackets.
e.g. Mg3(PO4)2
Mg = _____ P= ___ O= ___ 8

5. Coefficient
A. A coefficient is a number written in front of a chemical symbol and indicates that number of atoms of that element.
e.g. 3 C=
b. A coefficient is a number written in front of a chemical formula and indicates the number of molecules of that compound

6. Chemical Formula
Chemical Formula- combination of symbols that represents the atoms in a compound
Note: A coefficient multiplies the number of atoms of each element in the formula

7. Examples 2 H20 _____ molecules of H20 _____H (hydrogen)
_____ O (oxygen)

8. Examples Ca3(PO4)2 _______ molecules of Ca3(PO4)2 _______ Ca (Calcium)
_______ P (Phosphorus)
_______ O (oxygen)

9. Examples Pb (NO3)2 _______ molecules of Pb(NO3)2 _______ Pb (Lead)
_______ N (Nitrogen)
_______ O (Oxygen)