Amodeo Avogadro

Amodeo Avogadro came from a family of ecclesiastical lawyers, he was pushed into a legal career and got his bachelor’s degree in jurisprudence at 16 years old. At the age of 20 he received his doctorate in ecclesiastical law. Amedeo Avogadro was an exceptional lawyer, up but he showed curiosity in natural philosophy and began studies of math and physics. He then became a professor at the college of Vercelli. John Dalton said that the atoms of an element each had a different weight but did not have an easy way to prove this. Avogadro's number determines molar masses and atomic masses easily.[¹]

Insight and Influences

Amedeo Avogadro was born in Turin in 1776 to Count Filippo Avogadro and his wife Anna Vercellone. His first
Image courtesy of The First Chemist
scientific research in 1803, undertaken jointly with his brother Felice, was on electricity. In 1806 Avogadro was appointed demonstrator at the Academy of Turin, and in 1809 became professor of natural philosophy at the college of Vercelli. He married Felicita Mazzé, and they had a total of six children. Avogadro led an industrious life, and was a modest man, he was so modest that his work wasn’t noticed until after his death when Stanislao Cannizarro had to forcefully present it at a major conference. Working in isolation was the way Amedeo preferred to work, like many other famous scientist.

An important milestone in Avogadro’s law was John Dalton’s law of multiple proportions published in 1804 that led to the first table of weights of elements. In 1808 Joseph-Louis Gay-Lussac published his law for the combining volumes of gases, that says gases combine among themselves in very simple proportions of their volumes, and if the products are gases, their volumes are also in simple proportions. For instance, 1 liter of oxygen gas combines with 2 liters of hydrogen gas to form 2 liter of gaseous water. Above all Gay-Lussac's law was of great influence on Avogadro's historical publication of 1811 in which he enunciated his law. In his 1811 paper Avogadro discusses Gay-Lussac's law and Dalton’s atomic theory. He calculates from gas densities that the molecular weight of nitrogen is 13.238 times the molecular weight of hydrogen (the modern value is 14). Avogadro was the first to propose that the gaseous elements, hydrogen, oxygen, and nitrogen, are diatomic molecules. He deduced that a molecule of water contains a molecule of oxygen and two molecules of hydrogen. Dalton, who had assumed earlier that water is formed from a molecule each of oxygen and hydrogen, rejected Avogadro's and Gay-Lussac's laws.

Major Contributions

Amedeo Avogadro is usually identified with his work about how gases are made up of particles. Dalton had this idea before Lussac and before Avogadro, but decided that it was incorrect in addition to Lussacs thoughts. This time however the great John Dalton was wrong. The spark that started the fire was Dalton’s ideas of gases and atomic weights. He wrote several papers about how solids and liquids took in gas. He once said, “Why does not water admit its bulk of every kind of gas alike? This question I have duly considered, and though I am not able to satisfy myself completely I am nearly persuaded that the circumstance depends on the weight and number of the ultimate particles of the several gases.” This was the beginning of Dalton’s quest for answers for why elements weighed the same. Dalton came up with five basic building blocks of his theories. The first, that elements are made of tiny particles called atoms. Next, all atoms of one element are the same. Third, atoms of different elements are different, and can be told apart by their atomic weights. Fourth, atoms of one element can combine with atoms of other elements to form compounds. Lastly, atoms are the smallest particles, they can’t be created or destroyed, and they are only rearranged in a chemical reaction.

“Avogadro made the word molecule to mean the smallest part of an atom.” Avogadro was the first to prove that water is made up of two hydrogen atoms and one oxygen atom. He found this by using his own number, “that when the mass of a compound is equal to the molecular weight, the total number of molecules is always the same, equal to 1 mole”. If Avogadro had not have made his hypothesis chemistry would be far different than what it is today and would still be looking for someone to correct Dalton some two hundred years later.

Affect and Effect

Amedeo Avogadro recently gained a position on the professorial staff at Turin as the first ever chair for mathematical physics, after Napoleon Bonaparte’s occupation of northern Italy in 1815; it came under the rule of a kingdom named Piedmont-Sardinia. Avogadro became very involved in the revolutionary movements against the new king. When the university found out they relieved Avogadro from his position as a professor for the official reason that 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”. This however was not the real reason, the real reason was because he supported and was involved in the revolutionary’s plots. This along with political changing disbanded the chair. Later the chair would be reinstated in 1832 and two years later so would Avogadro, he would stay in this position until he retired in 1850.


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