Oxidation and Reduction OxidationReduction OxidationReduction reactions are electron

Oxidation and Reduction

Oxidation-Reduction • Oxidation-Reduction reactions are electron transfer reactions. • Also called Redox Reactions.

Oxidation: the loss of electrons increases Mg 0 Mg 2+ + 2 e 2 -8 -2 (half rxn) 2 -8 Mg lost 2 electrons = oxidized

Reduction: the gaining of electrons reduces S 0 + 2 e- S 22 -8 -6 (half rxn) 2 -8 -8 S gains 2 electrons = Reduction

Redox When oxidation and reduction both take place. **Electrons go from the metal to the nonmetal. Mg + S Mg. S (net equation) Mg lost electrons oxidation S gains electrons reduction

You can’t have one… without the other! • Reduction (gaining electrons) can’t happen without an oxidation to provide the electrons. • You can’t have 2 oxidations or 2 reductions in the same equation. Reduction has to occur at the cost of oxidation LEO the lion says GER! o s e GER! l e c t r o n s x i d a t i o n a i n l e c t r o n s e d u c t i o n

Another way to remember • OIL RIG x s o i s d e a t i o n e s a d i u n c t i o n

Review of Oxidation Numbers The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred. 1. Free elements (uncombined state) oxidation number = zero. Na, Fe, K, Pb, H 2, O 2, P 4 = 0 2. In compounds use periodic table and they add to zero. 2+ 2 - Fe O 3+ 2 - Fe 2 O 3 3. Polyatomic ions add to the charge on the ion. +5 -2 +5 N O 3 NO 3 + -6 = -1

Oxidation numbers of all the atoms in…? +4 -2 S O 2 +1 +6 -2 -2 Na 2 (SO 4) +4 -2 C O 3 2 -3 +1+1 -2 (NH 4)2 S

Oxidation 1. The oxidation number increases 2. Metals oxidize 3. LEO (less electrons = oxidation) 4. Reduction needs to take place for there to be oxidation

Reduction 1. The oxidation number decreases 2. Nonmetals reduce 3. GER (gain electrons = reduction) 4. Oxidation needs to take place for reduction

Old definition: Gaining oxygen = oxidation Losing oxygen = reduction