Amedeo Avogadro

About this figure

Amedeo Avogadro (1776-1856) was an Italian scientist, trained originally in law, who turned to the study of physics and chemistry and is remembered for the hypothesis that now bears his name. In an 1811 essay on determining the relative masses of the elementary molecules of bodies, Avogadro proposed that equal volumes of gases, at the same temperature and pressure, contain equal numbers of molecules, regardless of the identity of the gas.

This hypothesis allowed chemists, at least in principle, to distinguish atoms from molecules and to calculate relative molecular weights from gas densities, but it was largely overlooked for decades, in part because the atomic and molecular theories of the time remained unsettled and Avogadro's own writing attracted little notice outside Italy. The Italian chemist Stanislao Cannizzaro revived and championed Avogadro's hypothesis in the 1850s and 1860s, and it was subsequently adopted as one of the cornerstones of chemical theory.

The fixed number of particles in a mole of substance was later named Avogadro's number in his honor, though Avogadro himself never calculated this figure, which was determined by other scientists, notably Jean Perrin, long after his death. Avogadro spent much of his career as a professor of physics at the University of Turin. He died in Turin in 1856, receiving wide recognition for his hypothesis mostly after his death.

Written by Epoch Voices. Not the figure’s own words.