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Mole (mol)

Quantity: amount of substance · Category: SI base unit

The mole is the SI base unit of amount of substance. One mole of any substance contains exactly 6.02214076×10²³ elementary entities (atoms, molecules, ions, electrons, or other specified particles), a value fixed by the 2019 SI revision. The mole was previously defined as the amount of substance in exactly 12 g of carbon-12; that definition is now obsolete — the mole is defined by the fixed numerical value of the Avogadro constant.

Relation to SI

Exact: 1 mol = 6.02214076×10²³ entities (Avogadro constant)

Examples

  • 18.015 g of water contains ≈ 1 mol of H₂O molecules
  • 12.011 g of natural-abundance carbon contains ≈ 1 mol of C atoms (note: exactly 12 g of carbon-12 was the OLD definition; the mole is now defined via the Avogadro constant)
  • A dozen is to eggs as a mole is to atoms — a counting unit, not a mass