1. Oxidation and Reduction Chem 1061 – Tro, Chapter 4 Lance S. Lund

2. Assigning Oxidation Numbers 1.The oxidation number of an element is zero. 2.The oxidation number of an atom in a monoatomic ion equals the charge on the ion. 3.The oxidation number of oxygen is -2 in most of its compounds. Exception: In peroxides, the oxidation number of oxygen is -1. 4.The oxidation number of hydrogen is +1 in most of its compounds. Exception: In hydrides, the oxidation number of hydrogen is -1.

3. Assigning Oxidation Numbers 5.The oxidation number of fluorine is -1 in all of its compounds. Each of the halogens has an oxidation number of -1 in binary compounds, except when the other element is a halogen above it in the Periodic Table or the other element is oxygen. 6.The sum of oxidation numbers of the atoms in a compound is zero. The sum of the oxidation numbers of the atoms in a polyatomic ion equals the charge on the ion.

4. Determine the Oxidation Numbers Determine the oxidation numbers of each element in the following species: – K 2 SO 4 H 3 PO 4 – Cr 2 O 7 2- Br 2

5. Redox Reactions The Loss of Electrons is Oxidation – An element that loses electrons is said to be oxidized. The species in which that element is present in a reaction is called the reducing agent. The Gain of Electrons is Reduction – An element that gains electrons is said to be reduced. The species in which that element is present in a reaction is called the oxidizing agent.