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Life of
Amedeo Avogadro
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Famous Italians)
Count Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e
Cerreto (Turin August 9, 1776 Cerreto? July 9, 1856) -
better known as Amedeo Avogadro -was an Italian scientist
born in the Kingdom of Sardinia ad Piedmont, most noted for
his contributions to the theory of molarity and molecular
weight. The number of molecules in one mole is called
Avogadro's number is honor of him, as is Avogadro's law.
His family's business was the law, and Amedeo followed in
his father's footsteps earning a doctorate of law in 1796.
He graduated in ecclesiastical law at a very young age (20)
and began to practice. However, soon after he dedicated
himself to the study of physics and mathematics, his
preferred sciences, and in 1809 he started teaching them
(then called positive philosophy) at a liceo (high school)
in Vercelli (where his family had some properties).
He was
apparently well liked by his students, who appreciated is
impish sense of humor, and quickly settled down into a happy
marriage blessed with six sons. In his free time he did a
lot of reading and had a complete set of the current
scientific journals in his library printed in four different
languages.
During this 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 Lam?herie'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 mani?e de d?erminer les masses relatives des
molecules ??entaires des corps, et les proportions selon
lesquelles elles entrent dans ces combinaisons (complete
English text here: [1]
(http://webserver.lemoyne.edu/faculty/giunta/avogadro.html)
- First page: [2]
(http://www.accademiaxl.it/Library/Percorsi/images/Image52.jpg)).
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. Hence,
relative molecular masses can be calculated from the masses
of gas samples.
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 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. For
instance, John Dalton didn't consider this possibility.
Avogadro did not actually use the word "atom" as the words
"atom" and "molecule" were used almost without difference.
He considered that there were three kinds of "molecules,"
including an "elementary molecule" (our "atom"). Also, a
keener attention was given to the definition of mass, as
distinguished from weight.
In 1814 he published M?oire sur les masses relatives des
mol?ules des corps simples, ou densit? pr?um?s de leur gaz,
et sur la constitution de quelques-uns de leur compos?, pour
servir de suite ?l'Essai sur le m?e sujet, publi?dans le
Journal de Physique, juillet 1811 ([3]
(http://www.accademiaxl.it/Library/Percorsi/images/Image54.jpg)),
about gas densities.
In 1820 he became a professor of Turin's university; In 1821
he published another memoria, Nouvelles consid?ations sur la
th?rie des proportions d?ermin?s dans les combinaisons, et
sur la d?ermination des masses des mol?ules des corps and
little after M?oire sur la mani?e de ramener les compos?
organiques aux lois ordinaires des proportions d?ermin?s.
With suspicious enthusiasm, he took part in political
revolutionary movements of 1821 (against the king of
Sardinia), so two years later he was removed from his
position (or, as it was officially declared, the university
was very glad to allow this interesting scientist to take a
rest from heavy teaching duties, in order to be able to give
a better attention to his researches). However, over time
this political isolation was gradually reduced, since
revolutionary ideas were receiving increasing attention from
Savoy kings, up to 1848 when Charles Albert granted a modern
Constitution (Statuto Albertino). Well before this,
following the increasing attention to his works, Avogadro
had been recalled at Turin university in 1833, where he
taught for another twenty years.
In 1841 he completed and published his work in Fisica dei
corpi ponderabili, ossia Trattato della costituzione
materiale de' corpi, 4 volumes.
Very little is known about his private life and his
political activity; despite his unpleasant aspect (at least
as depicted in the rare images found), he was known as a
discreet tombeur de femmes although devoted to a sober life
and a religious man. He had six children. Several historical
studies would confirm that he had sponsored and helped some
Sardinian plotters who were organising a revolution in that
island, stopped at the very last moment by the concession of
Charles Albert's statute. Some doubts however remain,
considering the very little amount of evidence.
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.
The scientific society didn't reserve a great attention at
his theory, so Avogadro's hypothesis wasn't immediately
accepted when announced. Andr?Marie Amp?e too was able three
years later to achieve the same result by another method (in
his Sur la d?ermination des proportions dans lesquelles les
corps se combinent d'apr? le nombre et la disposition
respective des mol?ules dont leurs particules int?rantes
sont compos?s), but the same indifferent regard was given to
his theories as well.
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.
Unfortunately, in the performance of related experiments,
some inorganic substances showed exceptions to the law. 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. Not long after, in
his researches regarding dilute solutions (and the
consequent discovery of analogies between the behaviour of
solutions and gases), J. H. van 't Hoff added his final
consensus for the triumph of the Italian scientist, who
since then has been considered the founder of the
atomic-molecular theory.
In honor of Avogadro's contributions to the theory of
molarity and molecular weights, the number of molecules in
one mole was renamed Avogadro's number. Which is
approximately 6.02214199 ?1023.
But in his own
time, Avogadro's principle was seriously neglected.
Historians of science have several theories as to why this
should be so, as Avogadro was a respected scientist during
his life. One possibility was that a more famous scientist,
J. J. Berzelius, was strongly advocating his "dualism"
theory which explained compound substances (molecules?) on
the basis that one half of the compound had to have a
positive charge and the other half a negative charge (to
hold the two halves together). It was hard to see how two
atoms of oxygen in one of Avogadro's "molecules" could have
different charges.
But the real
reason is probably more prosaic. In the clannish world of
scientific discovery, it pays to be at the center of the
action. Avogadro was by this time a professor, and chairman,
of physical chemistry at the University of Turin, but in
Italy - far away from the major science centers of England,
Germany, France or even Sweden. He never got to rub
shoulders with the "great ones" of his day, so his ideas did
not receive the credit they deserved.
He was a
professor until his retirement at the age of 74. He died
on July 9th, 1856.
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Famous Italians)
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