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 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.
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
N
3-
O
2-
Br
1-
P
3-
Ne__0__
S
2-
H
1+
Al__3+__
C
4+
1+
Mg
2+
Ca 2+
Al
3+_
Li 1+
F
1-_