Mole
Definition and meaning of Mole in chemistry.
Mole is the SI base unit of amount of substance, defined as containing exactly 6.02214076 × 1023 elementary entities (such as atoms, molecules, or ions) of a given substance. It enables chemists to count atoms, molecules, or ions using measurable mass.
In more detail
This constant, 6.02214076 × 1023, is called Avogadro's number (or the Avogadro constant in modern SI terminology). One mole of any substance always contains the same number of particles, regardless of what those particles are, making it possible to convert between particle counts and measurable quantities like mass. This constant is essential for stoichiometry, allowing chemists to predict how much product forms or how much reactant is needed in a chemical reaction. For instance, 1 mole of carbon-12 atoms has a mass of approximately 12 grams. This was exact by definition before 2019, when the mole was defined so that 12 grams of carbon-12 contained exactly one mole of atoms. Since the 2019 SI redefinition fixed the numerical value of the Avogadro constant instead, the molar mass of carbon-12 is now an experimentally determined quantity extremely close to, but not exactly, 12 g/mol.
Key facts
| Avogadro's Number | 6.02214076 × 1023 particles |
|---|---|
| Symbol | mol |
| Standard Definition | Fixed exactly by the 2019 SI redefinition of the Avogadro constant (previously based on carbon-12: 12 g of carbon-12 = 1 mole of atoms) |
| Field | General Chemistry |
A sample containing 1 mole of water (H2O) consists of 6.02 × 1023 water molecules and has a mass of approximately 18 grams, since the molar mass of water is 18 g/mol.
Frequently asked questions
Why is the mole such an important unit in chemistry?
The mole connects the atomic scale to the laboratory scale. It allows chemists to count particles by measuring mass, since individual atoms and molecules are far too small to count directly.
Is the mole only used for molecules?
No. The mole is used to count any type of particle: atoms, molecules, ions, electrons, or formula units. What matters is that it always represents 6.02214076 × 1023 of whatever particle you are counting.