The document discusses the mole concept in chemistry. It defines the mole as the amount of a substance that contains as many elementary entities (atoms, molecules, ions, etc.) as there are atoms in exactly 12 grams of carbon-12. This number is known as Avogadro's number and is equal to 6.022×1023. The mole allows chemists to convert between the mass of a sample and the number of particles it contains. It provides a link between macroscopic and microscopic scales in chemistry. The mole is a central unit for quantitative chemical calculations and experiments.