How to Count Atoms

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)