Amedeo Avogadro - Biography, Works, Reactions of the Scientific Community, Named after him

Scientist, born in Turin, Piedmont, NW Italy. In 1811 he formulated the hypothesis, known as Avogadro's law, that equal volumes of gases contain equal numbers of molecules, when at the same temperature and pressure. The principle did not come to be accepted until the work of Cannizzaro in the 1850s. Avogadro became professor of physics at Turin (1834–59).

For the Bishop, see Albert Avogadro.

Lorenzo Romano Amedeo Carlo Avogadro, Count of Quaregna and Cerreto (August 9, 1776–July 9, 1856) was an Italian chemist, most noted for his contributions to the theory of molarity and molecular weight.

Biography

Amedeo Avogadro was born in Torino to a noble ancient family of Piedmont, Italy.

However over time, Avogadro's political isolation became less, as revolutionary ideas received increasing attention from Savoy kings, until in 1848 when Charles Albert granted a modern Constitution (Statuto Albertino).

Very little is known about Avogadro's private life and political activity although he seems to have led a sober and religious life.

Avogadro held public posts in statistics, meteorology, and weights and measures (he introduced decimal metric system in Piedmont) and was a member of the Royal Superior Council on Public Instruction.

In honour of Avogadro's contributions to the theory of molarity and molecular weights, the number of molecules in one mole was renamed Avogadro's number, NA.

Loschmidt first calculated the value of Avogadro's number, now called Avogadro's constant, which is still sometimes referred to as the Loschmidt number in German-language countries (Loschmidt constant now has another meaning).

Works

During his stay in Vercelli he wrote a concise note (memoria) in which he declared the hypothesis of what we now call Avogadro's law:

equal volumes of gases, at the same temperature and pressure, contain the same number of molecules;

This memoria he sent to De Lamétherie's Journal de Physique, de Chimie et d'Histoire naturelle and it was published in the edition of July 14, 1811 with the title Essai d'une manière de déterminer les masses relatives des molecules élémentaires des corps, et les proportions selon lesquelles elles entrent dans ces combinaisons .

Avogadro's Law implies that the relationship occurring between the weights of same volumes of different gases (at the same temperature and pressure) corresponds to the relationship between respective molecular weights.

Avogadro developed this hypothesis after Joseph Louis Gay-Lussac had published in 1808 his law on volumes (and combining gases). The greatest difficulty Avogadro had to resolve was the huge confusion at that time regarding atoms and molecules – one of the most important contributions of Avogadro's work was clearly distinguishing one from the other, admitting that simple particles too could be composed of molecules, and that these are composed of atoms.

In 1814 he published Mémoire sur les masses relatives des molécules des corps simples, ou densités présumées de leur gaz, et sur la constitution de quelques-uns de leur composés, pour servir de suite à l'Essai sur le même sujet, publié dans le Journal de Physique, juillet 1811 (), about gas densities.

In 1821 he published another memoria, Nouvelles considérations sur la théorie des proportions déterminées dans les combinaisons, et sur la détermination des masses des molécules des corps and little after Mémoire sur la manière de ramener les composès organiques aux lois ordinaires des proportions déterminées.

Reactions of the Scientific Community

The scientific community did not reserve great attention to his theory, so Avogadro's hypothesis was not immediately accepted when announced.

Only with studies by Gerhardt, Laurent and Williamson on organic chemistry, was it possible to demonstrate that Avogadro's law was indispensable to explain why same quantities of molecules, brought to a vapour state, have the same volume. The matter was finally concluded by Stanislao Cannizzaro, as announced at Karlsruhe Congress (1860, four years after Avogadro's death), where he explained that these exceptions happened because of molecular dissociations which occurred at certain temperatures, and that Avogadro's law could determine not only molar masses, but as a consequence, atomic masses too.

Clausius, by his kinetic theory on gases, was able to give another confirmation of Avogadro's law.

Named after him

Avogadro's number (the number of molecules in one mole) Avogadro's law Avogadro (lunar crater)