The Mole and Avogadro's Constant [H]

This lesson covers the mole concept and Avogadro's constant as required by the AQA GCSE Chemistry specification (4.3.1). This is Higher Tier only content. The mole is the chemist's unit for counting particles — atoms, molecules, ions, or formula units. Understanding how to convert between moles, mass, and Mr is essential for all higher-level quantitative chemistry calculations.

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What Is a Mole?

A mole is a unit of measurement used in chemistry to express amounts of a chemical substance. One mole of any substance contains exactly 6.02 x 10^23 particles. This number is called Avogadro's constant and is given the symbol NA.

Term	Symbol	Value
Mole	mol	The amount of substance that contains 6.02 x 10^23 particles
Avogadro's constant	NA	6.02 x 10^23 per mole

The mole allows chemists to count atoms and molecules by weighing them. Since individual atoms are far too small to count, the mole bridges the gap between the atomic scale and the laboratory scale.

Why 6.02 x 10^23?