Definition:Mole/Historical Note
Jump to navigation
Jump to search
Historical Note on Mole
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