Definition:Avogadro's Number/Historical Note

Historical Note on Avogadro's Number

The name Avogadro's number was coined in $1909$ by Jean Baptiste Perrin, who defined it as the number of molecules in exactly $16$ grams of oxygen.

In $1971$, Avogadro's number was redefined as the number of atoms in $0.012$ kilograms of carbon-$12$.

It was further redefined in $2019$ to have the fixed number $6.02214076 \times 10^{23}$, and to base the mole on that.