The mole concept is a key tool in chemistry that allows scientists to count tiny particles—like atoms, molecules, or ions—by weighing substances. Because these particles are incredibly small and numerous, counting them directly is impossible. Instead, chemists use the mole, which represents 6.022 × 10²³ particles (Avogadro’s number).

By using the molar mass of a substance (the mass of one mole in grams), chemists can convert between mass and number of particles. For example:

• 1 mole of oxygen gas (O₂) has a mass of 32 grams and contains 6.022 × 10²³ O₂ molecules.
• 18 grams of water (H₂O) is 1 mole and contains 6.022 × 10²³ water molecules.

This concept is essential for:

• Calculating how much of a substance is needed or produced in a reaction
• Balancing equations
• Preparing solutions with precise concentrations

In essence, the mole provides a bridge between the atomic world and laboratory-scale measurements, making chemical calculations accurate and practical.