Overview
This lecture explains the concepts of oxidation, reduction, and redox reactions, including historical and modern definitions, practical examples, and applications such as rust prevention.
Early Definition of Oxidation
- Oxidation was initially defined as the addition of oxygen to a substance.
- Examples: Magnesium reacting with oxygen forms magnesium oxide; iron reacting with oxygen forms iron oxide (rust).
Electron Transfer and Modern Definition
- Oxidation now means loss of electrons, not just gaining oxygen.
- Metals like magnesium and iron lose electrons and become positively charged ions during oxidation.
- Oxygen gains electrons and is reduced, becoming negatively charged.
Reduction Explained
- Reduction is gaining electrons.
- Gaining electrons adds negative charge, lowering the atom's overall charge.
- Mnemomics: "LEO the lion says GER" (Losing Electrons Oxidation, Gaining Electrons Reduction) or "OIL RIG" (Oxidation Is Losing, Reduction Is Gaining).
Redox Reactions
- Redox reactions involve both oxidation (electron loss) and reduction (electron gain).
- Not all redox reactions require oxygen; any electron transfer suffices.
- Example: Iron and sulfur react, iron is oxidized (loses electrons), sulfur is reduced (gains electrons).
Identifying Oxidation and Reduction
- Track changes in charges (oxidation state) to determine which element is oxidized or reduced.
- If charges do not change, the reaction is not a redox reaction.
- Example: Double displacement reactions where no charge changes occur are not redox reactions.
Covalent Bonds and Electronegativity
- In covalent bonds like carbon dioxide, electrons are shared but not equally.
- Oxygen is more electronegative and pulls electrons closer, so it is considered reduced.
- Carbon is left partially positive (oxidized).
Applications: Preventing Rust
- Rusting is iron oxidizing (losing electrons) to oxygen.
- Coating iron with a more reactive metal like zinc prevents rust; zinc oxidizes instead of iron, offering protection.
Key Terms & Definitions
- Oxidation — Loss of electrons by a substance.
- Reduction — Gain of electrons by a substance.
- Redox Reaction — A chemical reaction where oxidation and reduction both occur.
- Electronegativity — The tendency of an atom to attract shared electrons.
- Rust — Iron(III) oxide formed when iron reacts with oxygen and water.
Action Items / Next Steps
- Practice identifying oxidation and reduction in sample chemical reactions.
- Review the concept of oxidation states and charge changes in reactions.
- Read more about methods to prevent metal corrosion (rusting).