Reduction is the process where a chemical species gains electrons (⚡) or loses oxidation number (🔋).
In simple terms, think of electrons as coins: when a species receives coins, it becomes “more negative” and its oxidation number drops.
Gain of electrons:
\$A + n\,e^- \;\longrightarrow\; A^{n-}\$
Example: \$Fe^{3+} + e^- \;\longrightarrow\; Fe^{2+}\$
Here, iron(III) gains one electron to become iron(II).
Decrease in oxidation number:
The oxidation number of the species becomes more negative (or less positive).
Example: \$Zn + 2H^+ \;\longrightarrow\; Zn^{2+} + H_2\$
Zn starts at 0, ends at +2 (a decrease in oxidation number).
Imagine each atom has an “electron bank account”.
- When it receives electrons, its account balance increases (more negative charge).
- When it loses electrons, its balance decreases (more positive charge).
Reduction is like depositing money into the bank – the account balance goes up (more negative).
Oxidation is the opposite – withdrawing money, making the balance more positive.
| Tip | Why It Helps |
|---|---|
| Always check oxidation numbers before balancing. | It tells you which species are oxidised and which are reduced. |
| Use the electron transfer method for balancing. | Keeps track of electrons and ensures charge balance. |
| Remember the sign of ΔOxidation Number. | Negative Δ means reduction, positive Δ means oxidation. |