# Amedeo Avogadro: The scientist whose law led to Mole

## We are celebrating the birthday of the scientist who laid the foundation that helped us get the Avogadro number or the value of a mole.

Mole is one of the seven standards of the International System of Units, or the SI Units. Today, we celebrate the birth day of the scientist who laid the foundation that helped us get the famed Avogadro number, or the value of a mole. A mole is also used as the Avogadro constant in chemical calculations. The constant was named in honour of this scientist, Mr Amedeo Carlo Avogadro.

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Avogadro was an Italian scientist born on August 9 in 1776 in Turin. He is known for the molecular theory that is now called Avogadro's law.

What is Avogadro's law?

The modern definition of Avogadro’s Law isn’t as complicated as it sounds. To put it in simple terms, equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.

Essentially, keep the temperature and pressure of a gas constant, consider a hypothetical gas - an ideal gas that occupies negligible space and has no interactions and obeys the gas laws exactly - and equal volumes will give you the same number of volumes.

How much is one mole?

We measure the amount of a substance in mole. As we measure length in metre, time in seconds and weight in kilogram, the amount of a substance is measured in moles. One mole is the amount of particles present in a particular substance including atoms, molecules, ions or electrons.

The value of a mole is 6.02214076×10^23, which basically means that one mole of a substance contains this number of particles, although the weight may vary. That means that even though we have a constant number of particles in various substances, the weight of it differs from one to the other.

It is also called the Avogadro constant and is represented by the term, ‘NA’. Johann Josef Loschmidt first calculated the value of the Avogadro number.

But, you will be surprised to know that Avogadro’s original molecular theory based on Avogadro's law was not given enough attention when it was published initially. His theory was taken forward by various scientists including Johann Josef Loschmidt, who calculated the value of Avogadro number.

He also lost his job as a result of the political situation of his time. But, later he was reappointed and retired at the age of 74. He died at the age of 79 on July 9 in 1856.