Redox (reduction–oxidation, /ˈrɛdɒks/ RED-oks, /ˈrdɒks/ REE-doks[2]) is a type of chemical reaction in which the oxidation states of substrate change.[3]

  • Oxidation is the loss of electrons or an increase in the oxidation state of a chemical or atoms within it.
  • Reduction is the gain of electrons or a decrease in the oxidation state of a chemical or atoms within it.

Sodium and fluorine bonding ionically to form sodium fluoride. Sodium loses its outer electron to give it a stable electron configuration, and this electron enters the fluorine atom exothermically. The oppositely charged ions are then attracted to each other. The sodium is oxidized; and the fluorine is reduced.
Demonstration of the reaction between a strong oxidizing and a reducing agent. When a few drops of glycerol (mild reducing agent) are added to powdered potassium permanganate (strong oxidizing agent), a violent redox reaction accompanied by self-ignition starts.
Example of a reduction–oxidation reaction between sodium and chlorine, with the OIL RIG mnemonic[1]

There are two classes of redox reactions:

  • electron-transfer where only one (usually) electron flows from the reducing agent to the oxidant. This type of redox reaction is often discussed in term of redox couples and electrode potentials.
  • atom transfer, where an atom transfers from one substrate to another. For example, in the rusting of iron, the oxidation state of iron atoms increases as it converts to an oxide and simultaneously the oxidation state of oxygen decreases as it accepts electrons released by iron. Although oxidation reactions are commonly associated with the formation of oxides, other chemical species can serve the same function.[4] In hydrogenation, C=C (and other) bonds are reduced by transfer of hydrogen atoms.

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