Avogadro, Amedeo (1776–1856)

Italian physicist, one of the founders of physical chemistry, who proposed Avogadro's hypothesis on gases in 1811. His work enabled scientists to calculate Avogadro's number, and still has relevance for atomic studies.

Avogadro made it clear that the gas particles need not be individual atoms but might consist of molecules, the term he introduced to describe combinations of atoms. No previous scientist had made this fundamental distinction between the atoms of a substance and its molecules.

Avogadro was born in Turin, where he spent his whole academic career. He based most of his findings on a mathematical approach.

In 1809 Joseph Gay-Lussac had discovered that all gases, when subjected to an equal rise in temperature, expand by the same amount. From this Avogadro deduced his hypothesis.

Leading chemists of the day paid little attention to Avogadro's work, with the result that the confusion between atoms and molecules and between atomic weights and molecular weights continued for nearly 50 years.