CONCEPTS

# What is Avogadro’s number?

We explain to you what Avogadro’s number is, what is the value of this constant and a brief history of its invention.

1. ### What is Avogadro’s number?

In chemistry , the Avogadro number or Avogadro constant is called the number of constituent particles of a substance (usually atoms or molecules) that can be found in the amount of one mole of that substance. Said in simpler terms, it is a proportion factor that relates the mass (quantity of matter) typical of a substance and the mass present in a sample of it.

The accepted value of this constant is 6.022 140 857 (74) x1023 mol-1.

Currently, the term Avogadro Constant is used instead of “number”, since this term used to be preferred but was defined by different calculations. Jean Baptiste Perrin, in fact, initially defined it as the number of atoms in a mole of hydrogen (H); but then it was redefined as the number of atoms in 12 grams of carbon-12 , before it was generalized to be able to be applied proportionally to any type of substances.

Therefore, Avogadro’s number is a dimensionless value. In 1 gram of hydrogen there is an approximate 6.022 x 1023 hydrogen atoms, while in 12 grams of carbon-12 there are exactly the same amount of atoms. This is because atoms have different sizes depending on the element , of course. But it serves to know how much you have to use each substance to have an identical amount of atoms.

This is essential for experimental knowledge of chemistry . For example, to generate 1 mole of water (H2O) we must combine 1 mole of oxygen (6.022 x 1023 atoms) with 2 moles of hydrogen (2 x 6.022 x 1023 atoms). This, of course, in accordance with the measurements accepted by the International System (SI).

1. ### Avogadro Number History

The invention of this constant is attributed to Amadeo Avogadro , an early 19th-century Italian scientist, who first proposed in 1811 that a volume of a gas at a given pressure and temperature contains the same amount of atoms or molecules , regardless of The very nature of gas.

The Avogadro Number was however postulated in 1909 with that name, by the French physicist Jean Perrin, who would win the Nobel Prize in Physics in 1926 largely thanks to his efforts to determine the exact value of the Avogadro Constant using it various experimental techniques and  methods .