1. Writing Formulas Oxidation Numbers & Chemical Formulas Mrs. Wolfe

2. Review: How do you figure out the charge of an ion? What is the charge of Sodium? +1 Another word for Charge is OXIDATION NUMBER. + -

3. Is there a pattern of Oxidation Numbers on the Periodic Table? Time for a Worksheet: “Discovering Oxidation Numbers”!

4. +1 +2+3±4-3-2 0 Write the pattern in your notes!

5. There is a pattern of ions! METALS ARE POSITIVE! NONMETALS ARE NEGATIVE!

6. Practice Problems… What is the oxidation number of Aluminum? +3 What is the oxidation number of Iodine? Time for a worksheet: Oxidation Numbers

7. Writing Formulas Consider the formula BeCl 2 How many atoms of Beryllium are in that compound? 1 How many atoms of Chlorine? 2 WHY?

8. BeCl 2 Be 2 Cl 7 7

9. Cl -1 BeCl 2 Be +2 Cl -1 Be +2

10. Lithium & Fluorine What is the oxidation number for Lithium? +1 Fluorine? So how many atoms do you need of each element to make a compound? One of each! The formula is… LiF F -1 Li +1

11. LiF not FLi…why? You always write the METAL FIRST in a formula. Let’s try another one. Try to write a formula for Magnesium & Sulfur. MgS S -2 Mg +2

12. How about Magnesium + Chlorine? Magnesium’s oxidation # +2 Chlorine’s oxidation # Cl -1 Mg +2 Cl -1 MgCl 2 Time for some practice with Formula Writing!