1. The Meaning of Oxidation Reduction Reactions that take place in the presence of oxygen usually involve a process called oxidation. – In oxidation reactions, oxygen makes an atom that it binds with more positive (either through loss of electrons or unequal sharing of electrons) – oxygen becomes reduced as it becomes more negative. – together they form a redox reaction. the atom that becomes more positive is oxidized – known as the reducing agent the atom that becomes more negative is reduced – known as the oxidizing agent

2. Covalent example: CH 4 + 2O 2  CO 2 + 2H 2 O In this reaction Oxygen is reduced (becomes more negative) – starts with equal sharing of covalent electrons – holds electrons from C-O bond close – O is the oxidizing agent Carbon is oxidized (becomes more positive) – starts off holding shared C-H electrons close – becomes positive as a result of the C- O bond – C is the reducing agent general rule: – the atom gaining Oxygen is oxidized – the atom gaining H is reduced Redox

3. Ionic Example: Ba + Cl 2  BaCl 2 In this reaction Ba is Oxidized (becomes positively charged cation) – Ba loses 2e- to become Ba 2+ – reducing agent Cl is Reduced (becomes negatively charged anion) – each Cl gains 1e- to become Cl - – oxidizing agent

4. Processes leading to Redox Oxidation Reduction Complete loss of electronsComplete gain of electrons shift of electrons away from an atom (covalent bond) shift of electrons toward an atom (covalent bond) Gain of oxygenLoss of oxygen Loss of hydrogen (covalent compound)Gain of hydrogen (covalent compound) Increase in oxidation numberDecrease in oxidation number Examples of redox reactions: Combustion Corrosion Ion formation Most everything else!