Today it is very easy for us to define what an atom or molecule is. In the early days of science there was a lot of debate about this. It was Amedeo Avogadro who helped tell the difference between compounds, molecules and atoms.
You may have heard of Avogadro’s law or Avogadro’s number when studying about molecules. But what do you know of the person behind the law - Amedeo Avogadro. An Italian noble, he is most remembered for clearing up the confusion between an atom and a molecule.
His early years
Born in August 1776 in Turin, Italy, Avogadro was the son of a lawyer and senator in Piedmont, who was appointed as president of the Italian senate. He began his early years studying in Turin. Coming from a family of lawyers, it was natural for Amedeo to follow in his fathers footsteps. And when he was just 16, he earned a degree in law. Four years later, after completing his doctorate, he began to work as a lawyer.
Avogadro’s urge to study didn’t stop with his law degree. He took private tuitions in maths and physics and began to experiment in electricity. By 1806 he had become a demonstrator at Turin College. He then became a professor of natural philosophy at the Royal College at Vercelli. And later on followed it up by holding the position of chair of mathematics and physics at the University of Turin.
Avogadro’s biggest contribution to chemistry was his law on gases, which he first stated in 1811. His law explains that gases at equal volumes, temperatures and pressures will contain the same number of molecules. This means that molecular weights of any two gases are same as the ratio of density of two gases having the same temperature and pressure.
The difference between atoms and molecules
Avogadro actually had nothing to start with. During the time when he was forming his law of gases, atoms and molecules were still not properly defined. It is Avogadro who helped bring clarity to this issue by explaining that gases were of compounds of molecules. And that a molecule could be made of two or more atoms. Avogadro was the scientist who reasoned that when water boils and becomes water vapour, a molecule of oxygen splits into two atoms.
Imagine a number named after you. Exciting isn’t it? Avagadro’s number is not his school roll number. And no, it’s not his mobile number either. It has something to do with his work on atoms and molecules.
Avogadro's number is 6.0221415 × 1023
Originally called Avogadro’s number, it was later named Avogadro’s constant. It is the number of atoms in 12 grams of carbon-12. This number was not discovered by Avogadro, but it was because of his contribution to molecular theory the number was given his name.