Redox Reactions and Oxidation States 🔬

Introduction

• Electrons in chemistry are likened to money in capitalism.
  • The focus is on who has them, who wants them, and what they are willing to do to get them.
  • Electrons enable atoms to bond and form molecules, exchanging significant energy in the process.
• Not all chemical reactions involve electron exchange, e.g., acid-base reactions involving protons.
• Key reactions on Earth involve electron transfer between atoms, called oxidation-reduction or redox reactions.
• These reactions are derived from the words oxidation and reduction.
  • Oxidation: involves oxygen but not always and generally understood as losing electrons.
  • Reduction: means gaining electrons, despite the misleading terminology.

History and Terminology

• Early chemists named these reactions before modern understanding.
  • Antoine Lavoisier discovered that weight changes due to oxygen leaving a compound during heating.
  • Oxidation: substance loses electrons, despite increasing its oxidation state.
  • Reduction: substance gains electrons, despite decreasing its oxidation state.
• Mnemonic: OIL RIG (Oxidation Is Loss, Reduction Is Gain).

Importance of Redox Reactions

• Essential for processes like cellular respiration, photosynthesis, battery operation, and combustion.
• Tracking electron movement is crucial just like tracking money in transactions.

Oxidation States

• Useful system to assign electrons to atoms in a compound.
• Oxidation number: charge if an atom owned all its electrons exclusively.
• Rules for determining oxidation states:
  1. The oxidation state of an element in its standard state is zero.
  2. For a monoatomic ion, the oxidation state equals its charge (e.g., Fe²⁺ = +2).
  3. Oxygen typically has an oxidation state of -2, except in peroxides.
  4. Hydrogen typically has an oxidation state of +1.
  5. Fluorine always has an oxidation state of -1, other halogens are usually -1 unless bonded to more electronegative atoms.
  6. The sum of oxidation states in a neutral molecule is zero; for polyatomic ions, it equals the ion charge.

Example Reactions

• Haber Process: Extracting nitrogen from the air and combining it with hydrogen to form ammonia (NH₃).
  • Nitrogen (N₂) and hydrogen (H₂) start with oxidation state zero.
  • Ammonia has nitrogen with oxidation state -3 and hydrogen with +1.
  • Demonstrates nitrogen reduction (gain of electrons) and hydrogen oxidation (loss of electrons).
• Silver Mirror Reaction: Diammine silver reacts with an aldehyde to deposit metallic silver.
  • Silver reduction from +1 to 0, aldehyde carbon oxidation from +1 to +3.
  • Detailed balancing of half-reactions for clarity.

Summary

• Any electron transfer reaction is a redox reaction.
• Oxidation: loss of electrons; reduction: gain of electrons.
• Oxidation numbers help track electron movements.
• Practice examples: Haber process and silver mirror reaction.

Contributors

• Written by: [Authors]
• Chemical Consultant: Dr. Haiko Lagnèr
• Editing and Production Team: [Team Members]