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The Mole

What is the mole?

· Sarah Mitchell

Key facts

Symbol mol[1]
Quantity measured Amount of substance[1]
Exact number in 1 mole 6.022 140 76 × 10^23[1]
Entities counted Elementary entities (atoms, molecules, ions, specified particles)[2]
Fixed numerical value Avogadro constant (N_A)[1]

The mole is the SI unit of amount of substance, defined by an exact number of elementary entities: 6.022 140 76 × 10^23. It is used in chemistry to count atoms, molecules, ions, or other specified particles in a measurable way.

Context

The mole is the SI unit for amount of substance, containing exactly 6.022 140 76 × 10^23 specified elementary entities such as atoms, molecules, or ions [1]. This number is tied to the Avogadro constant, which was fixed in the 2018 redefinition [3]. The mole is a standard scientific unit for measuring large quantities of very small entities [2].

Documented claims

  • The mole was redefined in 2018 by fixing the Avogadro constant to exactly 6.022 140 76 × 10^23 mol^-1. [3]
  • The older definition of the mole was based on the number of atoms in 0.012 kilogram of carbon-12. [3]

Questions and answers

What does one mole contain?

One mole contains exactly 6.022 140 76 × 10^23 specified elementary entities, such as atoms or molecules [1].

How was the mole redefined?

In 2018, the mole was redefined by fixing the Avogadro constant to exactly 6.022 140 76 × 10^23 mol^-1 [3].

What is the older definition of the mole?

The older definition was the amount of substance containing as many elementary entities as there are atoms in 0.012 kilogram of carbon-12 [3].

Sources

  1. Mole | Definition, Number, & Facts — britannica.com (retrieved August 3, 2026)
  2. In Other Words: The Measure of a Mole — nigms.nih.gov (retrieved August 3, 2026)
  3. mole (mol) - NPL — npl.co.uk (retrieved August 3, 2026)

Sources last checked August 3, 2026. · More in Culture