Avogadro

Amedeo Carlo Avogadro (1776–1856) was an Italian scientist whose ideas helped define the relationship between the quantity of a substance and the number of its constituent particles. He is best known for Avogadro's hypothesis, proposed in 1811, which addressed the behavior of gases and the nature of molecules.

Avogadro's hypothesis states that equal volumes of gases, at the same temperature and pressure, contain the same number of molecules, regardless of the gas’s identity. This insight helped distinguish atoms from molecules and laid the groundwork for the concept of the mole and molecular theory. Although his ideas faced slow acceptance in his lifetime, they became foundational for modern chemistry, especially after later work linked Avogadro's hypothesis to atomic weights and stoichiometry.

Avogadro's constant, commonly called Avogadro's number, is the number of constituent particles in one mole of a substance. It is approximately 6.02214076 × 10^23 mol^-1, a value now fixed exactly by the International System of Units since 2019. This constant enables the conversion between macroscopic amounts of material and the number of atoms or molecules contained in them, underpinning quantitative chemistry and physics.

Today, Avogadro's contributions are recognized as central to atomic theory and chemical quantification. The term “Avogadro's number” is widely used in science to express the scale of particle counts in chemical reactions and molecular studies, reflecting Avogadro’s lasting impact on science.