Electrochemical Reaction - Chemical reaction that involves the flow of electrons.

Oxidation - Any process in which the oxidation number of an atom increases (becomes more positive).

Reduction - Any process in which the oxidation number of an atom decreases (becomes more negative).

Oxidation Number - The charge that an atom would have if the compound in which it were found were ionic.

See Assigning Oxidation Numbers

Redox Reaction (oxidation-reduction reaction) - A reaction in which at least one atom changes in oxidation state.

• Corrosion - A type of redox reaction in which a metal is destroyed.

  4 Fe(s) + 3 O_2(g) 2 Fe₂O₃ • 3 H₂O

• Metathesis Reaction - A reaction in which atoms are interchanged and there is no change in oxidation number.

To help remember oxidation and reduction, remember the following:

LEO goes GER

• Losing Electrons is Oxidation

• Gaining Electrons is Reduction

Don't confuse this with the following definitions:

• Oxidizing Agent - Causes oxidation; undergoes reduction (gains electrons).
• Reducing Agent - Causes reduction; undergoes oxidation (loses electrons).

Good Oxidizing Agents

• Atoms, ions, and molecules with large electron affinities.

  e.g.  F₂, Cl₂

• Compounds with large oxidation states.
  • WHY? - The electronegativity increases as oxidation state increases
  • Electronegativity - The tendency of an atom to draw electrons toward itself.

    e.g.  MnO₄^-, CrO₄^2-

Good Reducing Agents

• Active metals

  e.g.  Na, Mg, Al, Zn

• Metal hydrides

  e.g.  NaH, CaH₂

• H₂ can act as either:

  Oxidizing agent when it combines with metals.
  Reducing agent when it combines with nonmetals.

**In spontaneous redox reactions, stronger oxidizing and reducing agents are converted into weaker oxidizing and reducing agents.

Disproportionation Reaction - A reaction in which a single reactant undergoes both oxidation and reduction.

Next:  "Assigning Oxidation Numbers"