Amedeo Avogadro was an Italian physicist who originated the hypothesis that equal volumes of all gases, under the same pressure and temperature conditions, contain the same number of molecules. He made this hypothesis in 1811, and it has since been fully proven and is now known as Avogadro’s law. Avogadro was born on August 9th, 1776, in Turin, Italy, to an artistic family.
Avogadro practiced law and then studied physics and mathematics. He was appointed professor of physics at Vercelli in 1809. In 1811, he set forth his famous hypothesis, now known as Avogadro’s law. The law states that equal volumes of all gases at the same temperature and pressure contain the same number of molecules.
Avogadro’s law helped overcome flaws in John Dalton’s atomic theory. Avogadro also distinguished between an atom and a molecule, and made it possible to determine a correct table of atomic weights. The correction and standardization of atomic weights began in 1858 when Stanislao Cannizzaro, an Italian chemist, reminded other chemists about Avogadro’s work. The hypothesis was virtually ignored by chemists because when it was tested in 1881, appropriate temperatures were not used by other scientists. Avogadro’s number, stated as 6.0221367 x 10^23, states that a mole of any substance is that quantity of the substance that weighs (in grams) the same as its molecular weight.
For example, molecular oxygen has a weight of 32 grams (16 for each oxygen atom). One mole of oxygen weighs 32 grams. A mole of a substance always contains the same number of molecules, known as Avogadro’s law. Therefore, Avogadro’s law can be stated in terms of moles, namely that equal volumes of gases at the same temperature and pressure contain the same number of molecules. This can be achieved by simply weighing out an equal number of moles. Avogadro’s number holds true for all substances, regardless of their state.
