Oxidation Number

the combining ability of an atom

(how many electrons it needs to gain or lose to be

stable)

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

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 3 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.

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

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+

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+