Amedeo Avogadro

Amedeo Avogadro (1776–1856) was an Italian chemist whose 1811 hypothesis—that equal volumes of gases at the same temperature and pressure contain the same number of molecules—laid the cornerstone for molecular theory. His insight, now known as Avogadro’s law, clarified the distinction between atoms and molecules and enabled chemists to determine relative molecular weights. The Avogadro constant (≈6.022×10^23 particles per mole) bears his name, linking the microscopic world of atoms to the macroscopic measurements of chemistry. Though underappreciated in his lifetime, his work ultimately transformed stoichiometry and physical chemistry.