1. Oxidation Number the combining ability of an atom (how many electrons it needs to gain or lose to be stable)

2. How to find oxidation number: One step at a time! 1. Find the number of valence electrons Example: Na is in column 1 so it has 1 valence electron

3. How to find oxidation number: One step at a time! 2. Decide the easiest way for the atom to get a full outer energy level. Remember: 8 is great, but for hydrogen, 2 electrons will do to get stable! If an atom has 1, 2 or 3 valence electrons, it is easiest to give them away. If it has more than 4 it is easiest for the atom to get some more to make it stable. Example: Na has 1 valence electron so it is easiest to give it away.

4. How to find oxidation number: One step at a time! 3. Write the number of electrons the atom needs to give or get to become more stable. Example: Na needs 1

5. How to find oxidation number: One step at a time! 4. Add the sign… + if the atom gives away electrons - if the atom gets electrons Example: Na gives away so its number is 1+

6. OXIDATION NUMBER PRACTICE Key: Na _1+_B 3+ Cl 1- K 1+ Mg 2+ N 3- O 2- Br 1- Ca 2+ Al 3+_ P 3- Ne__0__S 2- Li 1+ F 1-_ H 1+ Al__3+__C 4+