What does a mole measure in chemistry?

A mole is a fundamental concept in chemistry used to measure the amount of substance. Specifically, one mole contains exactly 6.022 x 10²³ entities, which can be atoms, molecules, ions, or other particles. This number, known as Avogadro's number, allows chemists to convert between the number of particles and the mass of a substance, enabling the calculation of how many individual entities are present in a sample.

In practical terms, using moles allows scientists to work with manageable quantities of materials, as dealing directly with such large numbers of particles would be impractical. For example, when a chemist measures out one mole of water, they are working with approximately 18 grams, which corresponds to Avogadro's number of water molecules.

The concept of a mole is essential for stoichiometry, which is the calculation of reactants and products in chemical reactions. Thus, the mole is fundamental for understanding the quantitative aspects of chemistry, facilitating calculations that involve atomic and molecular scales.