The mole (symbol: mol) is the SI unit of amount of substance. It is defined as containing exactly 6.02214076 × 10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol⁻¹ and is called the Avogadro number.
In simpler terms:
- The Mole: A unit that measures the amount of a substance.
- The Defining Quantity: One mole contains exactly 6.02214076 × 10²³ elementary entities.
- Elementary Entities: These entities can be atoms, molecules, ions, electrons, other particles, or specified groups of particles. Crucially, the entities must be specified.
- Avogadro Constant (NA): The number 6.02214076 × 10²³ mol⁻¹ is known as the Avogadro constant, a fundamental constant in chemistry and physics.
Before the 2019 redefinition of the SI base units, the mole was defined as the amount of substance containing as many elementary entities as there are atoms in 0.012 kilogram of carbon-12. The current definition is more precise and independent of any physical artifact or substance.
Therefore, the definition emphasizes that the mole is a number – a specific count of entities – rather than a mass or volume.
