The concept of molar mass was introduced by the Italian chemist and physicist Amedeo Avogadro. Avogadro's hypothesis, proposed in 1811, stated that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules. This idea eventually led to the development of Avogadro's law and the concept of Avogadro's number.
Avogadro's law, formulated by the French chemist Joseph Louis Gay-Lussac in 1809, states that the volume of a gas is directly proportional to the number of molecules (or moles) present, when temperature and pressure are held constant.
By combining Avogadro's hypothesis with Avogadro's law, it became possible to relate the mass of a substance to the number of moles of particles it contains. This led to the introduction of the concept of molar mass, which is defined as the mass of one mole of a substance.
The term "molar mass" was not explicitly used by Avogadro himself, but his contributions laid the foundation for its development. The concept of molar mass became widely accepted and is now an essential part of chemical calculations and the understanding of stoichiometry. It provides a bridge between the macroscopic scale (mass) and the microscopic scale (number of particles or moles) in chemistry.