1. Chemical Formulas and Equations

2. Parts of a formula Coefficient: the number in front of the symbol, which tells you how many molecules there are. Subscript: The number after the symbol, which tells you how many atoms there are for each element.

3. Determining how many atoms Multiply the coefficient by the subscript Use a 1 for any coefficient or subscript that is missing

4. Example 5H 2 1. Coefficient: 2. Subscript: 3. Element: 4. How many atoms?

5. Example 5H 2 1. Coefficient: 5 2. Subscript: 2 3. Element: hydrogen 4. How many atoms? 5 x 2 = 10

6. Practice 1. 3 CO 2 2. N 2 O 3. 5MgCl 2 4. 2 C 6 H 12 O 6 Try the ones on the back of the page!

7. Practice 1. 3 CO 2 C = 3, O = 6 2. N 2 O N = 2, O = 1 3. 5MgCl 2 Mg = 5, Cl = 10 4. 2 C 6 H 12 O 6 C = 12, H = 24, O = 12 Try the ones on the back of the page!

8. Chemical equations A chemical equation is a short way to describe a chemical reaction Reactants: the starting materials in a chemical reaction (before the arrow) Products: the new substances made in a chemical reaction (after the arrow) Example: C + O 2 CO 2 Reactants: C (carbon) and O2 (oxygen) Products: CO2 (carbon dioxide)

9. Chemical equations continued What does the arrow mean? Yields or gives you What does the “+” mean? “and” Law of conservation of mass: Atoms are not created nor destroyed You have to have the same number of each element on both sides of the equation

10. Let’s practice Take out the last sheet you picked up on your way in Let’s do the first one together