Define reduction in terms of: (a) gain of electrons (b) a decrease in oxidation number

Chemical Reactions – Redox

What is Reduction?

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.

Two Ways to Define Reduction

1. 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).

2. 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).

Analogy: The Electron Bank

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.

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