Amedeo Avogadro did not directly determine the number of atoms (now known as Avogadro's number) during his lifetime. However, his work laid the foundation for understanding the concept and indirectly contributed to the determination of Avogadro's number by subsequent scientists.
Avogadro is best known for Avogadro's hypothesis, proposed in 1811, which stated that equal volumes of gases, at the same temperature and pressure, contain an equal number of particles. This hypothesis was significant because it suggested that the relative masses of gases could be compared based on their volumes.
Avogadro's hypothesis was later expanded upon by other scientists, such as Stanislao Cannizzaro, who used it to develop a method for determining atomic and molecular masses relative to a chosen standard. This paved the way for accurately comparing the masses of different elements and compounds.
The determination of Avogadro's number was achieved through the combination of various experimental techniques and theoretical advancements. One notable contribution came from Jean Baptiste Perrin, who performed precise measurements of Brownian motion in 1908. Perrin's work provided a direct link between macroscopic observables and the behavior of individual atoms or molecules.
Using Perrin's data and Einstein's theoretical explanation of Brownian motion, the physicist Jean Baptiste Perrin was able to calculate Avogadro's number in 1909. By relating the observed movement of particles to their mass and other physical properties, Perrin derived a value for Avogadro's number that was consistent with other experimental data.
In summary, Avogadro's hypothesis laid the groundwork for understanding the relationship between the volume, pressure, and number of particles in gases. This hypothesis, along with subsequent advancements in experimental techniques and theoretical models, ultimately led to the determination of Avogadro's number, which represents the number of atoms or molecules in one mole of a substance.