Today In Science History – July 9


Amedeo Avogadro

Amedeo Avogadro (1776-1856) Italian chemist known for his gas law and the constant that bears his name.

July 9 is the anniversary of the death of Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto, or as he is more commonly known: Amedeo Avogadro.

Avogadro was an Italian chemist known by students of science around the world. His gas law and the constant that bears his name is one of the first numbers a chemistry student memorizes. He was one of the first that suggested gas molecules in the air could be combinations of atoms bonded together. In spite of all this, in 1856, when Avogadro died, his work was barely acknowledged. He was actually part of a noble family from Piedmont, Italy. Avogadro was formally educated and served as a lawyer. He learned mathematics and chemistry through private lessons on his own time. He eventually held the chair of physical chemistry at the University of Turin.

Avogadro’s Law was based on the work of Gay-Lussac. Gay-Lussac demonstrated when volumes of gases combine at the same pressure and temperature, the volume of the products will be an integer multiple of the initial volumes. Avogadro took it a step further. He theorized equal volumes of gases at the same temperature and pressure would have the same number of molecules. This in turn led to the idea that the ratio of the relative atomic weights of two gases would be the same as the ratio of their densities at the same pressure and temperature.

Avogadro proposed gas molecules in the air were made up of ‘elementary molecules’ or what John Dalton was calling ‘atoms’. He felt this would explain why Gay-Lussac found the volume of water vapor was twice the volume of oxygen used to create it. The oxygen molecule was actually two elementary oxygen molecules joined together. This idea was generally ignored since people believed molecules are formed when two parts of opposite electric charge are attracted to each other. If there were two identical parts with the same charge, they should repel each other.

Some have suggested Avogadro’s work was often ignored because he was in Italy. Most chemists of note were from Germany, Sweden, France or England. These countries were at the forefront of chemical science, not Italy. It is disappointing his contributions to chemistry were not widely recognized until after his death. Eventually, much of what he said was true. His name is associated with the number of molecules or atoms found in one mole of a substance. Avogadro’s number is equal to 6.022 ×1023 mol−1. This is one of the first things a new chemistry student learns along with the name of the man.

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