Editing Amedeo Avogadro (section)

==Accomplishments==

In honour of Avogadro's contributions to molecular theory, the number of molecules per mole of a substance is named the [[Avogadro constant]], ''N''<sub>A</sub>. It is exactly {{physconst|NA|after=.}}  The Avogadro constant is used to compute the results of chemical reactions. It allows chemists to determine the amounts of substances produced in a given reaction to a great degree of accuracy.

[[Johann Josef Loschmidt]] first calculated the value of the Avogadro constant, the number of particles in one mole, sometimes referred to as the Loschmidt number in German-speaking countries ([[Loschmidt constant]] now has another meaning).

[[Avogadro's law]] states that the relationship between the masses of the same volume of all gases (at the same temperature and pressure) corresponds to the relationship between their respective molecular weights. Hence, the relative molecular mass of a gas can be calculated from the mass of a sample of known volume.

Avogadro developed this hypothesis after [[Joseph Louis Gay-Lussac]] published his law on volumes (and combining gases) in 1808. The greatest problem Avogadro had to resolve was the confusion at that time regarding atoms and molecules. One of his most important contributions was clearly distinguishing one from the other, stating that gases are composed of molecules, and these molecules are composed of atoms. (For instance, [[John Dalton]] did not consider this possibility.) Avogadro did not actually use the word "atom" as the words "atom" and "molecule" were used almost without difference. He believed that there were three kinds of "molecules", including an "elementary molecule" (our "atom"). Also, he gave more attention to the definition of [[mass]], as distinguished from [[weight]].

[[File:Avogadro - Mémoire sur les chaleurs spécifiques des corps solides et liquides, 1833 - 6060053 TOAS005003 00003.tif|thumb|''Mémoire'']]
In 1815, 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'' ("Note on the Relative Masses of Elementary Molecules, or Suggested Densities of Their Gases, and on the Constituents of Some of Their Compounds, As a Follow-up to the Essay on the Same Subject, Published in the Journal of Physics, July 1811") about gas densities.

In 1821 he published another paper, ''Nouvelles considérations sur la théorie des proportions déterminées dans les combinaisons, et sur la détermination des masses des molécules des corps'' (''New Considerations on the Theory of Proportions Determined in Combinations, and on Determination of the Masses of Atoms'') and shortly afterwards, ''Mémoire sur la manière de ramener les composès organiques aux lois ordinaires des proportions déterminées'' ("Note on the Manner of Finding the Organic Composition by the Ordinary Laws of Determined Proportions").

In 1841, he published his work in ''Fisica dei corpi ponderabili, ossia Trattato della costituzione materiale de' corpi'', 4 volumes.