Amadeo Avogadro was born in Turin, Italy 9th August, 1776. Avogadro was born into a family of established lawers and was therefore not surprisingly educated in law. Eventhough there was a prospect of a promising law career Avogadro was more interested in the natural sciences and chose to study maths and psysics in his spare time. In 1806 he became professer of natural philosophy at the college of Vercelli.
You have probaly heard of Avogadros number which defines that in any one mole of a compound there are 6.0221367×1023 molecules or atoms.
Even though it was not Avogadro himself who determined this number, it was his work and theories which caused this number and the idea of a mole to be introduced, hence the number bieng named after him.
To get an idea of the sheer enormity of Avogadros number, imagine if the earths surface was covered with 6.0221367×1023 cans of cola the density of cans would be over 200 miles deep!!
In chemistry at the time of Avogadro, it was proposed by Dalton that in the most common compound between two elements there were only one of each element. However this theory was questionable when looking at the work of Gay-Lussac, which produced results showing how one 'particle' of oxygen would react to form two 'particles' of water. Dalton tried to discredit Gay-Lussacs work because it under minded his own.
In 1811 Avogadro published a work stating that Dalton had not distinguished between atoms and molecules, and this way the reason why discrepencies aros in his theories and work, and in actual fact oxygen exists as the diatomic molecule O2.
Also in 1811 Avogadro published what is now known as Avogadros law, which states,
Avagodros theories were not really accepted at the time when he was alive, it wasn't untill a man called Cannizzaro presented Avagadros theories at a chemistry convention in 1860, four years after Avogadro died in 1856, that people really took notice.