Avogadro's number: interesting information

From the school course of chemistry we know that if we take one mole of a substance, then it will contain 6.02214084 (18) • 10 ^ 23 atoms or other structural elements (molecules, ions, etc.). For convenience, Avogadro's number is usually written in the following form: 6.02 • 10 ^ 23.

However, why is the constant Avogadro (in the Ukrainian language "Avogadro became") equal precisely to this value? The answer to this question in the textbooks is missing, and historians from chemistry offer a variety of versions. It seems that Avogadro's number has some secret meaning. After all, there are also magic numbers, where some include the number "pi", Fibonacci numbers, seven (in the east eight), 13, etc. We will fight the information vacuum. About who Amedeo Avogadro is, and why in honor of this scientist, in addition to the law he formulated, a constant was also found on the crater on the Moon, we will not speak. This is already written a lot of articles.

To be precise, Amedeo Avogadro did not deal with the calculation of molecules or atoms in a certain volume. The first to try to find out how many molecules of gas Contained in a given volume at the same pressure and temperature, was Josef Loschmidt, and it was in 1865. As a result of his experiments, Loschmidt came to the conclusion that in one cubic centimeter of any gas under ordinary conditions there are 2.68675 x 10 19 molecules.

Subsequently, a large number of independent ways of how to determine Avogadro's number was invented and since the results largely coincided, this once again spoke in favor of the actual existence of molecules. At the moment, the number of methods has exceeded 60, but in recent years, scientists are trying to further improve the accuracy of the assessment to introduce a new definition of the term "kilogram". For now, a kilogram is compared with the chosen material standard without any fundamental definition.

However, let us return to our question - why is this constant 6.022 • 10 ^ 23?

In chemistry, in 1973, for convenience in calculations it was suggested to introduce such a notion as the "amount of substance". The main unit for measuring the amount was the mole. According to the recommendations of IUPAC, the amount of any substance is proportional to the number of its specific elementary particles. The coefficient of proportionality does not depend on the type of substance, and Avogadro's number is its reciprocal.

For clarity, let's take an example. As is known from the definition of the atomic mass unit, 1 amu. Corresponds to one twelfth of the mass of one carbon atom of 12C and is 1.66053878 • 10 ^ (-24) grams. If we multiply 1 amu On the Avogadro constant, then it will be 1.000 g / mol. Now we take some chemical element, say, beryllium. According to the table, the mass of one beryllium atom is 9.01 amu. Let's count what is equal to one mole of atoms of this element:

6.02 x 10 ^ 23 mol-1 * 1.66053878x10 ^ (-24) grams * 9.01 = 9.01 grams / mol.

Thus, it turns out that the molar mass coincides numerically with the atomic mass .

The constant Avogadro was specially chosen so that the molar mass corresponded to an atomic or dimensionless value-the relative molecular (atomic) mass. It can be said that Avogadro's number owes its appearance, on the one hand, to the atomic unit of mass, and on the other hand to the common unit for comparing the mass-gram.