Oxidation-Reduction • Oxidation-Reduction reactions are electron transfer reactions. • Also called Redox Reactions.
Oxidation:the loss of electrons increases Mg0 Mg2+ + 2e- (half rxn) 2-8-2 2-8 Mg lost 2 electrons = oxidized
Reduction:the gaining of electrons reduces S0 + 2e- S2- (half rxn) 2-8-6 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 MgS (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! ose lectrons xidation ain lectrons eduction GER!
Another way to remember • OIL RIG s s xidation ose eduction ain
Review of Oxidation Numbers The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred. • Free elements (uncombined state) oxidation number = zero. Na, Fe, K, Pb, H2, O2, P4 = 0 • In compounds use periodic table and they add to zero. 2+ 2- 3+ 2- Fe O Fe2 O3 • Polyatomic ions add to the charge on the ion. +5 -2 +5 + -6 = -1 N O3 N O3 -
Oxidation numbers of all the atoms in…? +4 -2 +4 -2 S O2 C O3 2- +1 +6 -2 -2 -3 +1 +1 -2 Na2 SO4 ( ) (NH4)2S
Oxidation • The oxidation number increases • Metals oxidize • LEO (less electrons = oxidation) • Reduction needs to take place for there to be oxidation
Reduction • The oxidation number decreases • Nonmetals reduce • GER (gain electrons = reduction) • Oxidation needs to take place for reduction
Old definition: Gaining oxygen = oxidation Losing oxygen = reduction