Who came up with Avogadro's number?

Answer 1

Amedeo Avogadro, an Italian physicist, first proposed the concept in 1811, but it was Jean Perrin that specifically calculated the number through numerous methods and received a Nobel Prize in 1926.

Answer 2

According to Wikipedia, the Avogadro constant "is named after the early nineteenth-century Italian scientist Amedeo Avogadro, who, in 1811, first proposed that the volume of a gas (at a given pressure and temperature) is proportional to the number of atoms or molecules regardless of the nature of the gas. The French physicist Jean Perrin in 1909 proposed naming the constant in honor of Avogadro. "

Numerous scientists have been involved in the "development" of this number since knowing it requires measuring things. From the dates referred to above, you can see it was a hundred years between the time it was recognized as an essential quantity to be known in advancing our understanding that atoms and molecules exist as individual countable entities. This was important in quantifying early chemistry.

Answer 3

The number of Avogadro is the number of molecules in a mole of substance.
The value is 6,022 140 857(74).1o.e23.