Lorenzo Romano Amedeo Carlo Avogadro, (/ˌɑːvəˈɡɑːdroʊ/)
Quaregna and Cerreto (9 August 1776 – 9 July 1856),
was an Italian scientist, most noted for his contribution to molecular
theory now known as Avogadro's law, which states that equal volumes of
gases under the same conditions of temperature and pressure will
contain equal numbers of molecules. In tribute to him, the number of
elementary entities (atoms, molecules, ions or other particles) in 1
mole of a substance, 7023602214085700000♠6.022140857(74)×1023, is
known as the Avogadro constant, one of the seven SI base units and
represented by NA.
3 Response to the theory
4 See also
6 Further reading
7 External links
Avogadro was born at
Turin to a noble family of Piedmont-Sardinia in
the year 1776. That city, now part of Italy, was then of the Kingdom
He graduated in ecclesiastical law at the late age of 20 and began to
practice. 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 lived and had
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 Jean-Claude Delamétherie's Journal de
Physique, de Chimie et d'Histoire naturelle ("Journal of Physics,
Chemistry and Natural History", Piedmont at the time forming part of
the First French Empire).
In 1820, he became a professor of physics at the University of Turin.
Turin was now the capital of the restored Savoyard Kingdom of Sardinia
under Victor Emmanuel I. Avogadro was active in the revolutionary
movement of March 1821. As a result, he lost his chair in 1823 (or, as
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").
Eventually, King 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
Little is known about Avogadro's private life, which appears to have
been sober and religious. He married Felicita Mazzé and had eight
children.[dubious – discuss] 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.
He died on 9 July 1856.
In honor of Avogadro's contributions to molecular theory, the number
of molecules in one mole was named "Avogadro's number", NA or
"Avogadro's constant". It is approximately
Avogadro's number is used to
compute the results of chemical reactions. It allows chemists to
determine amounts of substances produced in a given reaction to a
great degree of accuracy.
Johann Josef Loschmidt
Johann Josef Loschmidt first calculated the value of Avogadro's
number, often referred to as the Loschmidt number in German-speaking
Loschmidt constant now has another meaning).
Avogadro's Law states that the relationship between the masses of the
same volume of same 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
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 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
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 proposed a very similar theory three years later (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
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
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
Rudolf Clausius, with his kinetic theory on gases proposed in 1857,
provided further evidence for 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.
Avogadro (lunar crater)
^ Guareschi, Icilio (1911), "
Amedeo Avogadro e la sua opera
scientifica", Opere scelte di Amedeo Avogadro, Turin: Accademia delle
scienze, pp. i–cxl .
^ "Avogadro". Random House Webster's Unabridged Dictionary.
Hinshelwood, C. N.; Pauling, L. (1956), "Amedeo Avogadro", Science
(published Oct 19, 1956), 124 (3225), pp. 708–713,
Cavanna, D. (1956), "Centenary of the death of Amedeo Avogadro",
Minerva farmaceutica (published Jun 1956), 5 (6), pp. 134–7,
Crosland, M. P. (1970), "Avogadro, Amedeo", Dictionary of Scientific
Biography, 1, New York: Charles Scribner's Sons, pp. 343–350,
Morselli, Mario. (1984). Amedeo Avogadro, a Scientific Biography.
Kluwer. ISBN 90-277-1624-2.
Review of Morselli's book: Pierson, S. (1984), "Avogadro and His Work:
Amedeo Avogadro", Science (published Oct 26, 1984), 226 (4673),
pp. 432–433, Bibcode:1984Sci...226..432M,
doi:10.1126/science.226.4673.432, PMID 17799933
Pierre Radvanyi, "Two hypothesis of Avogadro", 1811 Avogadro's article
analyzed on BibNum (click 'Télécharger').
Wikimedia Commons has media related to Amedeo Avogadro.
Wikisource has the text of the 1911 Encyclopædia Britannica article
Avogadro, Amedeo, Conte di Quaregna.
Amedeo Avogadro at Open Library
Scientists whose names are used in physical constants
Isaac Newton (gravitational constant)
Charles-Augustin de Coulomb
Charles-Augustin de Coulomb (Coulomb's constant)
Amedeo Avogadro (Avogadro constant)
Michael Faraday (Faraday constant)
Johann Josef Loschmidt
Johann Jakob Balmer
Joseph Stefan (Stefan–Boltzmann constant)
Ludwig Boltzmann (Boltzmann constant, Stefan–Boltzmann constant)
Johannes Rydberg (Rydberg constant)
Joseph John Thomson
Max Planck (Planck constant, reduced Planck constant, Planck length,
Niels Bohr (Bohr radius)
Edwin Hubble (Hubble constant)
Brian David Josephson
Klaus von Klitzing
List of scientists whose names are used as SI units
List of scientists whose names are used as SI units and non SI units
ISNI: 0000 0000 8391 4641
BNF: cb12500597w (data)