Oxidation vs Reduction
Oxidation
Oxidation is the loss of electrons by an atom, ion, or molecule during a reaction. The oxidized species ends up with a higher (more positive) oxidation number. Remember it with the mnemonic OILRIG: Oxidation Is Loss.
Example: In the reaction of sodium with chlorine, each sodium atom loses one electron to become Na+ — the sodium is oxidized.
Reduction
Reduction is the gain of electrons by an atom, ion, or molecule during a reaction. The reduced species ends up with a lower (more negative) oxidation number. Remember it with the mnemonic OILRIG: Reduction Is Gain.
Example: In the same sodium-chlorine reaction, each chlorine atom gains one electron to become Cl- — the chlorine is reduced.
Key differences
| Aspect | Oxidation | Reduction |
|---|---|---|
| Electron movement | Loses electrons (OIL = Oxidation Is Loss). | Gains electrons (RIG = Reduction Is Gain). |
| Change in oxidation number | Oxidation number increases (becomes more positive or less negative). | Oxidation number decreases (becomes more negative or less positive). |
| Agent terminology | Called the reducing agent — it gives electrons away and is itself oxidized. | Called the oxidizing agent — it takes electrons and is itself reduced. |
| Everyday example | Sodium metal losing one electron to become Na+. | Chlorine gaining one electron to become Cl- in the same reaction. |
| In combustion | Fuels are oxidized when they burn; the fuel donates electrons. | Oxygen is reduced when it burns fuel; oxygen accepts electrons. |
| In batteries and cells | Removing electrons from food molecules (glucose) to extract energy in cells. | Receiving electrons at the other electrode or in the electron transport chain. |
Two common traps: (1) the oxidizing agent is the substance that gets REDUCED — it causes oxidation in the other reactant, not in itself; (2) 'oxidation' does not require oxygen at all — it simply means losing electrons (the term survives from the earliest oxygen-based reactions). Also, oxidation and reduction never occur alone: every electron lost by one species is gained by another, which is why these are called redox reactions.