Definition:Mole

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Mole

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

It is defined as exactly Avogadro's number of particles, that is, $6 \cdotp 02214 076 \times 10^{23}$.


The specific type of particle under discussion must be specified.

They are usually the elementary units of a particular substance under discussion.

However, 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 units are molecules)
gram-atom (for a substance whose elementary units 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 $2018$.

At that point, the mole was defined to be exactly Avogadro's number of particles.


Hence a mole of carbon-$12$ atoms has a mass of almost exactly $12$ grams.


Sources