View source for Amedeo Avogadro

{{Short description|Italian scientist (1776–1856)}}
{{pp-semi-indef}}
{{Use dmy dates|date=July 2025}}
{{Infobox scientist
| name              = Amedeo Avogadro
| image             = Amadeo Avogadro.png
| caption           = 
| birth_name        = Amedeo Carlo Avogadro
| birth_date        = {{Birth date|1776|8|9|df=y}}
| birth_place       = [[Turin]], [[Kingdom of Sardinia (1720–1861)|Kingdom of Sardinia]]
| death_date        = {{Death date and age|1856|7|9|1776|8|9|df=y}}
| death_place       = [[Turin]], [[Kingdom of Sardinia (1720-1861)|Piedmont-Sardinia]]
| nationality       = [[Italians|Italian]]
| residence         = 
| fields            = [[Chemistry]]
| workplaces        = [[University of Turin]]
| alma_mater        = 
| doctoral_advisor  = 
| academic_advisors = 
| doctoral_students = 
| notable_students  = 
| known_for         = [[Avogadro's law]]<br>[[Avogadro constant]]
| author_abbrev_bot = 
| author_abbrev_zoo = 
| influences        = 
| influenced        = 
| awards            = 
| signature         = Avogadro-sig.png
}}

'''Lorenzo Romano Amedeo Carlo Avogadro, Count of [[Quaregna]] and [[Cerreto Castello|Cerreto]]'''<ref>{{citation | first = Icilio | last = Guareschi | contribution = Amedeo Avogadro e la sua opera scientifica | title = Opere scelte di Amedeo Avogadro | url = http://gallica.bnf.fr/ark:/12148/bpt6k90576f.langEN | publisher = Accademia delle scienze | location = Turin | year = 1911 | pages = i–cxl}}.</ref> ({{IPAc-en|ˌ|æ|v|ə|ˈ|ɡ|ɑː|d|r|oʊ}},<ref>{{Cite dictionary |url=http://www.lexico.com/definition/Avogadro,+Amedeo |archive-url=https://web.archive.org/web/20220824192140/https://www.lexico.com/definition/avogadro,_amedeo |url-status=dead |archive-date=2022-08-24 |title=Avogadro, Amedeo |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}}</ref> <small>also</small> {{IPAc-en|US|ˌ|ɑː|v|-}},<ref>{{cite web|url=https://www.collinsdictionary.com/dictionary/english/avogadro|title=Avogadro|work=[[Collins English Dictionary]]|publisher=[[HarperCollins]]|access-date=7 August 2019}}</ref><ref>{{Cite Merriam-Webster|Avogadro|access-date=7 August 2019}}</ref><ref>[http://www.dictionary.com/browse/avogadro "Avogadro"]. ''[[Random House Webster's Unabridged Dictionary]]''.</ref> {{IPA|it|ameˈdɛːo avoˈɡaːdro|lang}}; 9 August 1776{{snd}}9 July 1856) was an [[Italian people|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 ratio of the number of elementary entities ([[atom]]s, [[molecule]]s, [[ion]]s or other particles) in a substance to its [[amount of substance]] (the latter having the unit [[mole (unit)|mole]]), {{physconst|NA|ref=no}}, is known as the [[Avogadro constant]].  This constant is denoted ''N''<sub>A</sub>, and is one of the seven defining constants of the [[SI]].

==Biography==
[[File:Avogadro, Amedeo – Saggio di teoria matematica della distribuzione dell'elettricità sulla superficie dei corpi conduttori, 1844 – BEIC 6060302.jpg|thumb|''Essay on the mathematical theory of the distribution of electricity on the surface of conducting bodies'', 1844]]

Amedeo Avogadro was born in [[Turin]] to a noble family of the [[Kingdom of Sardinia (1720–1861)|Kingdom of Sardinia]] (now part of [[Italy]]) in the year 1776. 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''),<ref>{{cite journal |last1=Aglio |first1=Linda S. |last2=Litvak |first2=Eva A. |last3=Desai |first3=Sukumar P. |title=History of anaesthesia |journal=European Journal of Anaesthesiology |date=January 2016 |volume=33 |issue=1 |pages=1–3 |doi=10.1097/EJA.0000000000000356|pmid=26627677 }}</ref> and in 1809 started teaching them at a ''liceo'' (high school) in [[Vercelli]], where his family lived and had some 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 a manner  of 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 [[Jean-Claude Delamétherie]]'s ''Journal de Physique, de Chimie et d'Histoire naturelle'' ("Journal of Physics, Chemistry and Natural History").

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 (1720–1861)|Kingdom of Sardinia]] under [[Victor Emmanuel I of Sardinia|Victor Emmanuel I]]. Avogadro was active in the [[Piedmont insurrection|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 of Savoy|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.{{Dubious |Number of kids |reason=Some sources say seven kids and some say six. |date=March 2016}} 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.

==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.

==Response to the theory==
The scientific community did not give great attention to Avogadro's theory, and it was not immediately accepted. [[André-Marie Ampère]] proposed a very similar theory three years later (in his ''{{lang|fr|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 contradictions. 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 of Italy|Victor Emmanuel III]] attended, and Avogadro's great contribution to chemistry was recognised.

[[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 theory#Avogadro|atomic-molecular theory]].

==See also==
* [[Avogadrite]] (mineral)
* [[Avogadro (crater)|Avogadro]] ([[lunar crater]])

==References==
{{Reflist}}

==Further reading==
* {{Citation
|pmid = 17757602
|last1=Hinshelwood
|first1=C. N.
|last2=Pauling
|first2=L.
|publication-date=Oct 19, 1956
|year=1956
|title=Amedeo Avogadro
|volume=124
|issue=3225
|periodical=Science
|pages=708–13
|doi = 10.1126/science.124.3225.708
|bibcode = 1956Sci...124..708H }}
* {{Citation
|pmid= 13369233
|last=Cavanna
|first=D.
|publication-date=Jun 1956
|year=1956
|title=Centenary of the death of Amedeo Avogadro
|volume=5
|issue=6
|periodical=Minerva Farmaceutica
|pages=134–37
}}
* {{Citation
  | last = Crosland
  | first = M. P.
  | title = Avogadro, Amedeo
  | encyclopedia = [[Dictionary of Scientific Biography]]
  | volume = 1
  | pages = 343–50
  | publisher = Charles Scribner's Sons
  | location = New York
  | year = 1970
  | isbn = 0-684-10114-9
  | postscript = .
 }}
* Morselli, Mario. (1984). ''Amedeo Avogadro, a Scientific Biography.'' Kluwer. {{ISBN|90-277-1624-2}}.
** Review of Morselli's book: {{Citation
|last=Pierson
|first=S.
|publication-date=Oct 26, 1984
|year=1984
|title=Avogadro and His Work: Amedeo Avogadro
|volume=226
|issue=4673
|periodical=[[Science (journal)|Science]]
|pages=432–33
|doi = 10.1126/science.226.4673.432
|pmid = 17799933
|bibcode = 1984Sci...226..432M }}
* Pierre Radvanyi, "Two hypothesis of Avogadro", 1811 Avogadro's article analyzed on ''[https://www.bibnum.education.fr/chimie/theorie-chimique/les-deux-hypotheses-d-avogadro-en-1811 BibNum] {{Webarchive|url=https://web.archive.org/web/20140717131359/https://www.bibnum.education.fr/chimie/theorie-chimique/les-deux-hypotheses-d-avogadro-en-1811 |date=2014-07-17 }}'' (click 'Télécharger').

==External links==
{{commonscat}}
{{EB1911 poster|Avogadro, Amedeo, Conte di Quaregna}}

* {{OL author|2392708A}}

{{Scientists whose names are used in physical constants}}

{{Authority control}}

{{DEFAULTSORT:Avogadro, Amedeo}}
[[Category:1776 births]]
[[Category:1856 deaths]]
[[Category:Scientists from Turin]]
[[Category:Italian chemists]]
[[Category:Fluid dynamicists]]
[[Category:Academic staff of the University of Turin]]
[[Category:Scientists from the Kingdom of Sardinia]]