Definition:Mole
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
- 1978: A.P. French and Edwin F. Taylor: An Introduction to Quantum Physics ... (previous) ... (next): $1$: Simple models of the atom: $\text {1-3}$: The Electrical Structure of Matter
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): mole
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): mole