Lecture Notes: Electron Transfer and Redox Reactions

Overview

• Redox (reduction-oxidation) reactions involve the transfer of electrons between reactants.
• Oxidation: Loss of electrons. Example: Substance A loses an electron.
• Reduction: Gain of electrons. Example: Substance B gains an electron.
• Oxidation and reduction occur simultaneously.

Key Concepts

• OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons).
• A redox reaction can be broken into two half-reactions:
  • Oxidation Half-Reaction: Electrons are removed from the oxidized species.
  • Reduction Half-Reaction: Electrons are added to the reduced species.

Example Reaction: Zinc and Copper

• Zinc: Oxidized by losing electrons and forming Zn²⁺ ions.
• Copper: Reduced by gaining electrons and forming elemental copper.
• Oxidizing Agent: Copper 2+ ion (gains electrons, causes another to oxidize).
• Reducing Agent: Zinc metal (loses electrons, causes another to reduce).

Oxidation Numbers

• Used to identify which species is oxidized or reduced.
• Rules for determining oxidation numbers:
  • Elemental state: 0 oxidation number.
  • Group 1 metals: +1, Group 2 metals: +2.
  • Halogens: usually -1, Oxygen: usually -2.
  • Sum of oxidation numbers in compounds must equal the compound's charge.
• Oxidation: Increase in oxidation number, more positive.
• Reduction: Decrease in oxidation number, more negative.

Reactivity Trends

• Metals: Tend to lose electrons and be oxidized.
  • Group 1 metals are very reactive, oxidizing rapidly.
  • Reactivity increases down a group and decreases across a period.
• Non-Metals: Tend to gain electrons and be reduced.
  • Reactivity increases up a group and across a period.

Activity Series

• A list of elements in order of decreasing reactivity.
• Metals at the top are strong reducing agents, easily oxidized.
• Non-metals like hydrogen and carbon can be included for reference.

Summary

• Redox reactions involve electron transfer.
• Oxidation: Loss of electrons, gain of oxygen, or loss of hydrogen.
• Reduction: Gain of electrons, gain of hydrogen, or loss of oxygen.
• Half-equations illustrate oxidation and reduction separately.
• Reactivity trends help predict which species are oxidized or reduced.
• Understanding oxidation numbers and reactivity trends is crucial for analyzing redox reactions.