Monday 11 July 2022

avogadro’s number

First outlined in his treatise on the molecular content of gases published on this day in 1811, Lorenzo Romano Amedeo Carlo Avogadro, Count of Quaregna and Cerreto, posited that the volume of a gas—at a given temperature and pressure—is proportional to the number of atoms or molecules in that volume whatever the kind of gas. The law or value named in his honour was first presented in a public forum by fellow scientist Stanislao Cannizzaro at the Karlsruhe Congress on Atomic Weights, four years after Avogadro’s death—with later developments and refinements from Josef Loschimdt and Jean Baptiste Jean Perrin. Defined initially as the number of molecules in sixteen grams of oxygen (the molar mass, SI unit the Mole from the German Molekรผl as a measure of substance, a count of particles), corresponding to the inverse of its relative atomic mass, and derives the constant N = 6,022 140 76 × 1023. This led to insights in fluid dynamics, ideal gases and the concept of absolute zero in terms of temperature and atomic excitement.