Amedeo Avogadro Conte di Quaregna

1776-1856

Italian Chemist

Amedeo Avogadro was an Italian lawyer, chemist, and physicist. He is best known for determining what is known as Avogadro's number, a physical and chemical constant used extensively in chemistry and physics calculations, including those involving gases.

The son of a lawyer and senator, Avogadro was born in 1776 in Turin, Italy. Avogadro began his career by earning a doctorate in law in 1796 and working as a lawyer for three years. In 1800 he began studying mathematics and physics with a private tutor, deciding to make his career in natural science instead of politics as was expected of him. He was appointed a professor of natural philosophy at the College of Vercelli in 1809, later earning an appointment as professor of mathematical physics.

Inspired by the work of Alessandro Volta (1745-1827), Avogadro began working on some problems in physics with his brother, Felice. Their work in this area earned Avogadro a nomination to the Royal Academy of Science of Turin, a great honor. This recognition gained him a position as demonstrator at the Royal College of the Provinces and convinced him that his future was in science rather than law.

Avogadro's most important accomplishment, however, was the research leading to his hypothesis that equal volumes of gas at a given temperature contain the same number of molecules. Avogadro identified this number as 6.023 × 10²³ molecules in one gram molecule (or mole) of any given substance. Although taken for granted today, this was revolutionary and controversial at the time and was not accepted until 50 years after Avogadro's death.

Avogadro was attempting to explain an observation made by Joseph Gay-Lussac (1778-1850) that combining equal volumes of gas under some circumstances did not lead to any measurable increase in the total gas volume. Avogadro explained this by positing that the chemical reactions formed another gas and that equal volumes of any gas at the same temperature and pressure, regardless of chemical composition, contain the same number of molecules. This observation also led to better estimates of the relative weights of a variety of gases, including hydrogen and oxygen. Avogadro's hypothesis also helped to explain other oddities noticed by Gay-Lussac, such as the fact that equal volumes of gas under changing conditions (i.e., changes in temperature, pressure, or volume) behave identically.

There are several reasons that Avogadro's research was so long neglected. He was not well known as a meticulous experimentalist and he failed to support his paper with solid data, leaving his results open to interpretation. In addition, he published his results in relatively minor journals that were not well known and, therefore, were easily overlooked or discounted. On top of that, his language lacked clarity, leading to errors in interpretation of his results. And, finally, the results of his work, if believed, promised to overturn the work of other, better known researchers. Thus, it was simply easier to ignore his work and accept the status quo.

In addition to his scientific research, Avogadro was a devoted family man, having six sons with his wife Felicita, the Countess Avogadro. Unlike Avogadro, his children took an interest in law, government, and the military.

Two years after his death, a colleague again presented Avogadro's work to the scientific community, showing that it helped to explain and solve some outstanding problems at that time. Given a more careful reading, Avogadro's work was acknowledged as accurate and valuable, earning him proper recognition at last. Avogadro is now regarded as one of the founders of modern chemistry and his famous number is used and taught as one of the cornerstones of chemical theory.

P. ANDREW KARAM