MSU Gallery of Chemists' Photo-Portraits and Mini-Biographies

Lorenzo Romano Amedeo Carlo Avogadro di Quaregua e di Cerreto

1776-1856

Amedeo Avogadro, born in Turin, then capital of the Sardinian States, first studied and practiced the law, but his brilliance, intense curiosity and constant adherence to strict logic led to an interest in the physical sciences. In 1820 he became professor of physics at the University of Turin. In 1821 he published (in French) his famous hypothesis, that equal volumes of gases at the same conditions of temperature and pressure contain the same number of molecules. He distinguished atoms from molecules, and proposed that oxygen, nitrogen and hydrogen (among others) had diatomic molecules. Avogadro's number, 6.023 x 10²³, is the number of molecules in one gram-molecular weight of a substance. In part because he worked in isolation, the tremendous significance of Avogadro's work was not recognized until nearly half a century after it was first published. The photograph, the only one known, is from a death mask.