Valency — যোজনী

Definition

Valency is an atom's combining power: the number of electrons it must lose, gain or share to reach a full outer shell. Group 1 metals like sodium have valency 1, Group 2 metals like magnesium valency 2, and Group 14 carbon uses all four outer electrons for a valency of 4. Many transition metals show variable valency — iron is 2 in $\mathrm{FeCl_{2}}$ but 3 in $\mathrm{FeCl_{3}}$ — and radicals such as $\mathrm{SO_{4}}$²⁻ act as a single unit with valency 2. Valency is what decides the formula of every compound.

For example

Water is $\mathrm{H_{2}O}$ because oxygen's valency is 2 and hydrogen's is 1; ammonia is $\mathrm{NH_{3}}$ because nitrogen's valency is 3 — the little numbers always balance out.

Elements this touches

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