# Definition:Mole

## Mole

The mole is the SI base unit of amount of substance.

It is defined as exactly $6 \cdotp 02214 076 \times 10^{23}$ particles.

The specific type of particle under discussion must be specified.

They usually include:

atoms (of a specified element)
molecules (of a specified substance)
ions (of a specified type)
electrons
photons

and so on, but (as long as the particles are more-or-less identical), there is no specific limitation to what a mole may be applied to.

A beloved teacher of chemistry at a certain $\mathsf{Pr} \infty \mathsf{fWiki}$ editor's school, when covering the subject, would habitually spend some time discussing a mole of cricket balls.

### Symbol

$\mathrm {mol}$

The symbol for the mole is $\mathrm {mol}$.

Its $\LaTeX$ code is \mathrm {mol} .

## Also known as

Terms formerly used for a mole include:

gram-molecule (for a substance whose elementary entities are molecules)
gram-atom (for a substance whose elementary entities are atoms)

## Examples

### Water

$1$ mole of water has a mass of (approximately) $18$ grams.

## Historical Note

The definition of the mole was adopted in November $2018$ as one of the seven SI base units.

The previous definition was the number of atoms in $12$ grams of carbon-$12$.

The original definition was as the mass in grams of a substance equal to its molecular weight, with atoms of hydrogen taken to be $1$.

The definition evolved, via a definition based upon oxygen-$16$, to the carbon-$12$ definition, which was the standard until $2018$.