Amedeo Avogadro

Amedeo Avogadro Italian physicist who originated the

hypothesis that the equal volumes of all gasses, under the

same pressure and temperature conditions, contain the

same number of molecules. Avogadro made this hypothesis

in 1811. It has since been fully proven and is now known as

Avogadro’s law.

Avogadro was born in Turin, Italy, an August 9th,

1776, 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 stated that equal volumes of all gasses 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


6.0221367 x10 23

Avogadros number stated 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 molecules

--the Avogadro’s law—as a mole of any substance.

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 by simply weighing out an equal number of

moles. Avogadros number itself holds true for all

substances, what ever there state.