Amedeo Avogadro

• Born: 9 August 1776
• Birthplace: Turin, Piedmont, Italy
• Died: 9 July 1856
• Best Known As: The guy they named Avogadro's Number after

Name at birth: Lorenzo Romano Amedeo Carlo Avogadro

Italian physicist Amedeo Avogadro put forth the hypothesis that equal volumes of gases under the same conditions of pressure and temperature contain the same number of particles. Trained as a lawyer, Avogadro turned to the study of science and spent most of his career as Chair of Mathematical Physics at Turin. Although he published widely on subjects in physics and chemistry, he is most famous for building on the work of French chemist Joseph Louis Guy-Lussac (1778-1850) with the 1811 publication of his hypothesis, and the idea that gases are made up of atoms or combinations of atoms (molecules) and can be quantified. Although his work was largely ignored during his lifetime, by the 1880s it was universally accepted, thanks to Stanislao Cannizzaro, who created a table of atomic weights based on Avogadro's work. Later physicists and chemists determined the value of "Avogadro's Number," the number of gas molecules in one mole (the atomic or molecular weight in grams), as 6.022 x 10²³.

In 1787 Avogadro inherited his father's title as Count of Quaregna.

Amedeo Avogadro, Comte de Quarenga

National Archives

[b. Turin, Piedmont (Italy), August 9, 1776, d. Turin, July 9, 1856]

In 1811 Avogadro proposed that equal volumes of gas at the same temperature and pressure contain the same number of molecules. Avogadro himself coined the word "molecule" to mean the smallest part of a compound. On the basis of his law Avogadro became the first to show that water is H²O -- that is, composed of molecules of two atoms of hydrogen and one of oxygen. The related concept, called Avogadro's number, is that when the mass of a compound in grams is equal to the molecular weight, the total number of molecules is always the same, equal to 1 mole.

The Italian physicist and chemist Lorenzo Romano Amedeo Carlo Avogadro, Conte di Quaregna e di Cerreto (1776-1856), authored the hypothesis known as Avogadro's law, which ultimately clarified the foundations of molecular chemistry and physics.

Born in Turin on Aug. 9, 1776, Amedeo Avogadro came from an ancient legal family, whose name derived from the Latin de advocatis (concerning the law). He took a degree in philosophy in 1789, a baccalaureate in jurisprudence in 1792, and a doctorate in ecclesiastical law a few years later.

After several years of legal experience, Avogadro found his true avocation in the study of the physical sciences. Though largely self-taught, he achieved an extensive knowledge of the then-expanding studies of matter in the gaseous state. In 1809 he was appointed professor of physics in the Royal College at Vercelli. Up to that time his only scientific paper had concerned a topic in the new field of electricity.

His Great Memoir

In July 1811 Avogadro published his memoir in the Paris Journal de physique. He began by drawing attention to the discovery by the French chemist Joseph Louis Gay-Lussac that when gases combine they do so in simple integral proportions by volume. Gay-Lussac supplied the experimental evidence to generalize this property of volume ratios for all gases; that is, two volumes of ammonia (NH₃) are composed of one volume of nitrogen and three volumes of hydrogen, and so forth for many similar cases of simple, integral proportions.

On the basis of this type of evidence, Avogadro drew the logical conclusion that the number of "integrant molecules" in all gases is always the same for equal volumes. He also concluded that the ratios of the masses of the molecules are the same as those of the densities of the different gases at equal temperature and pressure and that the relative number of molecules in a given compound is given at once by the ratio of volumes of the gases that form it.

In a supplementary paper sent to the Journal de physique in 1814, Avogadro deduced the correct formulas for COCl₂, H₂S, and CO₂, and from postulating an analogy between carbon and silicon he asserted the correct composition of silica, SiO₂. From available data he calculated approximately correct atomic weights for carbon, chlorine, and sulfur. He contributed massively to an understanding of the properties and reactions of the new and "changerous" element fluorine. He published these and related findings in a four-volume work entitled Fisica de' corpi ponderabili, ossia trattato della constituzione generale de' corpi (1837-1841). This book influenced Michael Faraday's great career of discovery.

The simplicity and clarity of Avogadro's views, though cited by leading scientists, such as André Marie Amp'e, were not compelling to the majority of contemporary chemists. This lack of interest was due in part to the novelty of the atomic theories which had been presented to the world a few years before by John Dalton; furthermore, the methodological temper of the times, deeply experimentalistic and empirical, prevented careful consideration of a purely logical inference from chemical facts unsupported by masses of laboratory data.

Another confusing aspect of the Avogadro memoir was the use of the ambiguous term "molecule." Not only did this conflict with the vigorous Newtonian atomism of the English and French schools, but it implied a sequence of chemical reactions for which no decisive evidence was forthcoming. Dalton, for example, had postulated that water was formed by the simple addition of the element hydrogen to the element oxygen, or H + O → HO, whereas the correct process implicit in Avogadro's hypothesis was 2H₂+ O₂ (in the molecular form) → 2H₂O.

Other Activities

When the first Italian chair in mathematical physics was established at the University of Turin in 1820, Avogadro received the professorship. Two years later, because of the turmoil gripping the country, the chair was suppressed. Avogadro returned to his position in 1834 and held it until his retirement in 1850. He married Donna Felicita Mazzi, by whom he had six sons. Two sons rose to positions of distinction: Luigi, who became general of the Italian army, and Felici, who became president of the Court of Appeal.

Avogadro also served Italy as a competent and honest civil servant. He held positions in the National Bureau of Statistics, helped to establish a national meteorological service, and in 1848 became a member of the Superior Council on Public Instruction. Modest and retiring, he was indifferent to honors and scrupulously avoided those public struggles for priority which were a characteristic of Continental scientific society in the mid-19th century.

Some indication of the fundamental nature of Avogadro's law may be seen in the fact that when modern thermodynamic theory was established at the end of the 19th century, the great German scientist and eventual Nobel laureate Walter Nernst entitled his textbook Theoretical Chemistry from the Standpoint of Avogadro's Rule and Thermodynamics.

Further Reading

A discussion of Avogadro's life and work appears in J. R. Partington, A History of Chemistry, vol. 4 (1964). See also Sir William Augustus Tilden, Famous Chemists: The Men and Their Work (1921); Eduard Farber, The Evolution of Chemistry: A History of Its Ideas, Methods and Materials (1952; 2d ed. 1969); Henry M. Leicester and Herbert S. Klickstein, eds., A Source Book in Chemistry, 1400-1900 (1952); and Isaac Asimov, A Short History of Chemistry: An Introduction to the Ideas and Concepts of Chemistry (1965).

Additional Sources

Morselli, Mario, Amedeo Avogadro, a scientific biography, Dordrecht; Boston: D. Reidel Pub. Co.; Hingham, MA: Sold and distributed in the U.S.A. and Canada by Kluwer Academic Publishers, 1984.

This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate. (May 2008)

"Avogadro" redirects here. For the Bishop, see Albert Avogadro. For the lunar crater, see Avogadro (crater).

Amedeo Avogadro
Born	August 9, 1776(1776-08-09) Turin, Italy
Died	July 9, 1856 (aged 79)
Fields	Physics
Institutions	University of Turin
Known for	Avogadro's law Avogadro constant

Lorenzo Romano Amedeo Carlo Avogadro di Quaregna (Quaregga) e di Cerreto, Count of Quaregna (or Quaregga) and Cerreto (9 August 1776 – 9 July 1856) was an Italian savant. He is most noted for his contributions to molecular theory, including what is known as Avogadro's law. In tribute to him, the number of elementary entities (atoms, molecules, ions or other particles) in 1 mole of a substance, 6.02214179(30)×10²³, is known as the Avogadro constant.

Contents 1 Biography 2 Accomplishments 3 Response to the theory 4 Further reading 5 See also

Biography

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

He graduated in ecclesiastical law at the early age of 20 and began to practise. Soon after, he dedicated himself to physics and mathematics (then called positive philosophy), and in 1809 started teaching them at a liceo (high school) in Vercelli, where his family had property.

In 1811, he published an article with the title Essai d'une manière de déterminer les masses relatives des molécules élémentaires des corps, et les proportions selon lesquelles elles entrent dans ces combinaisons ("Essay on Determining the Relative Masses of the Elementary Molecules of Bodies and the Proportions by Which They Enter These Combinations"), which contains Avogadro's hypothesis. Avogadro submitted this essay to a French journal, De Lamétherie's Journal de Physique, de Chimie et d'Histoire naturelle (Journal of Physics, Chemistry and Natural History) so it was written in French, not Italian. (Note: In 1811, northern Italy was under the rule of the French Emperor Napoléon Bonaparte.)

In 1820, he became professor of physics at the University of Turin. After the downfall of Napoléon in 1815, northern Italy came under control of this kingdom.

He was active in the revolutionary movements of 1821 against the king of Sardinia (who became ruler of Piedmont with Turin as his capital). As a result, he lost his chair in 1823 (or the university officially declared, it was "very glad to allow this interesting scientist to take a rest from heavy teaching duties, in order to be able to give better attention to his researches")^{[citation needed]}.

Eventually, Charles Albert granted a Constitution (Statuto Albertino) in 1848. Well before this, Avogadro had been recalled to the university in Turin in 1833, where he taught for another twenty years.

Little is known about Avogadro's private life, which appears to have been sober and religious. He married Felicita Mazzé and had six children.

Some historians suggest that he sponsored some Sardinian revolutionaries, who were stopped by the announcement of Charles Albert's constitution.

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

In honor of Avogadro's contributions to molecular theory, the number of molecules in one mole was named Avogadro's number, N_A or "Avogadro's constant". It is approximately 6.0221415 × 10²³. Avogadro's number is used to compute the results of chemical reactions. It allows chemists to determine the exact amounts of substances produced in a given reaction.

Johann Josef Loschmidt first calculated the value of Avogadro's number, often referred to as the Loschmidt number in German-speaking countries (Loschmidt constant now has another meaning).

Accomplishments

Avogadro's Law states that the relationship between the masses of the same volume of different 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 sample of known volume.

Avogadro developed this hypothesis after Joseph Louis Gay-Lussac had published in 1808 his law on volumes (and combining gases). 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, more attention was given to the definition of mass, as distinguished from weight.

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 ("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") ([1]), 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.

Response to the theory

The scientific community did not give great attention to his theory, so Avogadro's hypothesis was not immediately accepted. André-Marie Ampère achieved the same results three years later by another method (in his Sur la détermination des proportions dans lesquelles les corps se combinent d'après le nombre et la disposition respective des molécules dont leurs particules intégrantes sont composées -- On the Determination of Proportions in which Bodies Combine According to the Number and the Respective Disposition of the Molecules by Which Their Integral Particles Are Made), but the same indifference was shown to his theory as well.

Only through studies by Charles Frédéric Gerhardt and Auguste Laurent on organic chemistry was it possible to demonstrate that Avogadro's law explained why the same quantities of molecules in a gas have the same volume.

Unfortunately, related experiments with some inorganic substances showed seeming exceptions to the law. This was finally resolved by Stanislao Cannizzaro, as announced at Karlsruhe Congress in 1860, four years after Avogadro's death. He explained that these exceptions were due to molecular dissociations at certain temperatures, and that Avogadro's law determined not only molecular masses, but atomic masses as well.

In 1911, a meeting in Turin commemorated the hundredth anniversary of the publication of Avogadro's classic 1811 paper. King Victor Emmanuel III attended. Thus, Avogadro's great contribution to chemistry was recognised.

Rudolf Clausius, with his kinetic theory on gases, gave another confirmation of Avogadro's Law. Jacobus Henricus van 't Hoff showed that Avogadro's theory also held in dilute solutions.

Avogadro is hailed as a founder of the atomic-molecular theory.

Further reading

• Hinshelwood, C. N.; Pauling, L. (1956), "Amedeo Avogadro", Science 124 (3225): 708–713, 1956 Oct 19, doi:10.1126/science.124.3225.708, PMID:17757602, PMID 17757602 
• Cavanna, D. (1956), "Centenary of the death of Amedeo Avogadro", Minerva farmaceutica 5 (6): 134–7, 1956 Jun, PMID:13369233, http://www.ncbi.nlm.nih.gov/pubmed/13369233 
• Crosland, M. P. (1970). "Avogadro, Amedeo". Dictionary of Scientific Biography. 1. New York: Charles Scribner's Sons. pp. 343-350. ISBN 0684101149. 
• Morselli, Mario. (1984). Amedeo Avogadro, a Scientific Biography. Kluwer. ISBN 9027716242.

• Review of Morselli's book: Pierson, S. (1984), "Avogadro and His Work: Amedeo Avogadro", Science 226 (4673): 432–433, 1984 Oct 26, doi:10.1126/science.226.4673.432, PMID 17799933 

See also

Wikisource has the text of the 1911 Encyclopædia Britannica article Avogadro, Amedeo, Conte di Quaregna.

• Avogadro (lunar crater)
• Avogadro's constant

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