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7.1 Oxidation-Reduction • Electrochemistry • Oxidation Numbers: A System for Tracking Electrons • Oxidation and Reduction • Agents Cause Electron Transfer 7.1 Oxidation-Reduction Electrochemistry Electrochemistry is the study of the interconversion of chemical and electrical energy. Reactions that involve electron transfer are called oxidation-reduction reactions or redox reactions for short. 7.1 Oxidation-Reduction Oxidation Numbers: A System for Tracking Electrons The oxidation number is the real or apparent charge of an atom or ion when all bonds in the species containing the atom or ion are considered to be ionic. 7.1 Oxidation-Reduction Oxidation Numbers: A System for Tracking Electrons Rules for Assigning Oxidation Numbers: 1. 2. 3. 4. Atoms in the elemental form = 0 Monatomic ions = the ion’s charge Oxygen = −2 (except in peroxides = −1 and OF2 = +1) Hydrogen = +1 (except in metal hydrides = −1) 7.1 Oxidation-Reduction Oxidation Numbers: A System for Tracking Electrons Rules for Assigning Oxidation Numbers (Continued): 5. Oxidation numbers in compounds must sum to zero. 6. Oxidation numbers in polyatomic ions must sum to the ion charge. 7. Always assign the more electronegative element a negative oxidation number. 8. In a compound or ion containing more than 2 elements, the element written furthest to the right takes its most common oxidation number. 7.1 Oxidation-Reduction Oxidation and Reduction LEO says GER Losing Electrons is Oxidation. Gaining Electrons is Reduction. A decrease in oxidation number is reduction. An increase in oxidation number is oxidation. 7.1 Oxidation-Reduction Agents Cause Electron Transfer A species that is reduced acts as an oxidizing agent. In other words, oxidizing agents get reduced. A species that is oxidized acts as a reducing agent. In other words, reducing agents get oxidized.