Biography & Contributions

Amedeo Avogadro [Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto] was an Italian scientist born on August 09, 1776 – died on July 09, 1856. Avogadro was best known for his discovery of molecular theory and Avogadro's law, Avogadro constant.

Avogadro is chiefly remembered for his molecular hypothesis, first stated in 1811, in which he claimed that equal volumes of all gases at the same temperature and pressure contain the same number of molecules. He used this hypothesis further to explain the French chemist Joseph-Louis Gay-Lussac’s law of combining volumes of gases by assuming that the fundamental units of elementary gases may actually divide during chemical reactions.

It also allowed for the calculation of the molecular weights of gases relative to some chosen standard. Avogadro and his contemporaries typically used the density of hydrogen gas as the standard for comparison.

In 1811 he provided the correct molecular formula for water, nitric and nitrous oxides, ammonia, carbon monoxide, and hydrogen chloride. Three years later he described the formulas for carbon dioxide, carbon disulfide, sulfur dioxide, and hydrogen sulfide. He also applied his hypothesis to metals and assigned atomic weights to 17 metallic elements based upon analyses of particular compounds that they formed.

Avogadro used the EVEN hypothesis to interpret gas densities and assign molecular weights. EVEN implies that the density of a gas at a given temperature and pressure depends only on the weight of its molecules. Avogadro supposed that since the reported gas density of oxygen was 15 times that of hydrogen, the molecular weight of oxygen was 15 times that of hydrogen.

Avogadro constant is the number of constituent particles, usually atoms or molecules that are contained in the amount of substance given by one mole. It has the dimension of reciprocal amount of substance. Avogadro's constant has the value 6.02214129×1023Avogadro's number is a dimensionless quantity and has the numerical value of the Avogadro constant given in base units.

Avogadro's Law states that the relationship between the masses of the same volume of same gases corresponds to the relationship between their respective molecular weights.

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