What is avogadro equal to? Atomic mass unit

Avogadro's law

At the dawn of the development of atomic theory (), A. Avogadro put forward a hypothesis according to which, at the same temperature and pressure, equal volumes of ideal gases contain same number molecules. Later it was shown that this hypothesis is a necessary consequence kinetic theory, and is now known as Avogadro's law. It can be formulated as follows: one mole of any gas at the same temperature and pressure occupies the same volume, under normal conditions equal 22,41383 . This quantity is known as the molar volume of a gas.

Avogadro himself did not estimate the number of molecules in a given volume, but he understood that this was a very large value. The first attempt to find the number of molecules occupying a given volume was made in the year J. Loschmidt. From Loschmidt’s calculations it followed that for air the number of molecules per unit volume is 1.81 10 18 cm −3, which is approximately 15 times less true meaning. Eight years later, Maxwell gave a much closer estimate of “about 19 million million million” molecules per cubic centimeter, or 1.9 10 19 cm −3. In fact, 1 cm³ ideal gas at normal conditions contains 2.68675·10 19 molecules. This quantity was called the Loschmidt number (or constant). Since then it has been developed big number independent methods for determining Avogadro's number. The excellent agreement between the obtained values ​​provides strong evidence of the actual number of molecules.

Measuring a constant

Data in this article is as of December 2011.

The officially accepted value for Avogadro's number today was measured in 2010. For this, two spheres made of silicon-28 were used. The spheres were obtained at the Leibniz Institute for Crystallography and polished at the Australian Center for Precision Optics so smoothly that the heights of the protrusions on their surface did not exceed 98 nm. For their production, high-purity silicon-28 was used, isolated in Nizhny Novgorod Institute Chemistry of High-Pure Substances of the Russian Academy of Sciences from silicon tetrafluoride, highly enriched in silicon-28, obtained at the Central Mechanical Engineering Design Bureau in St. Petersburg.

Having such almost ideal objects, it is possible to high accuracy count the number of silicon atoms in the ball and thereby determine Avogadro's number. According to the results obtained, it is equal to 6.02214084(18)×10 23 mol −1 .

Relationship between constants

• Through the product of Boltzmann's constant, the Universal Gas Constant, R=kN A.
• Faraday's constant is expressed through the product of the elementary electric charge and Avogadro's number, F=eN A.

see also

Notes

Literature

• Avogadro's number // Great Soviet Encyclopedia

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See what "Avogadro's number" is in other dictionaries:

- (Avogadro’s constant, symbol L), a constant equal to 6.022231023, corresponds to the number of atoms or molecules contained in one MOLE of a substance ... Scientific and technical encyclopedic dictionary

Avogadro's number- Avogadro konstanta statusas T sritis chemija apibrėžtis Dalelių (atomų, molekulių, jonų) skaičius viename medžiagos molyje, lygus (6.02204 ± 0.000031)·10²³ mol⁻¹. santrumpa(os) Santrumpą žr. Priede. priedas(ai) Grafinis formatas atitikmenys:… … Chemijos terminų aiškinamasis žodynas

Avogadro's number- Avogadro konstanta statusas T sritis fizika atitikmenys: engl. Avogadro's constant; Avogadro's number vok. Avogadro Constante, f; Avogadrosche Konstante, f rus. Avogadro's constant, f; Avogadro's number, n pranc. constante d'Avogadro, f; nombre… … Fizikos terminų žodynas

Avogadro's constant (Avogadro's number)- the number of particles (atoms, molecules, ions) in 1 mole of a substance (a mole is the amount of substance that contains the same number of particles as there are atoms in exactly 12 grams of the carbon isotope 12), denoted by the symbol N = 6.023 1023. One of ... ... Beginnings modern natural science

- (Avogadro's number), number structural elements(atoms, molecules, ions or other parts) in units. number of va in va (in one pier). Named in honor of A. Avogadro, designated NA. AP is one of the fundamental physical constants, essential for determining plural... Physical encyclopedia

- (Avogadro’s number; denoted by NA), the number of molecules or atoms in 1 mole of a substance, NA = 6.022045(31) x 1023 mol 1; name named A. Avogadro... Natural science. encyclopedic Dictionary

- (Avogadro’s number), the number of particles (atoms, molecules, ions) in 1 mole in va. It is designated NA and is equal to (6.022045 ... Chemical encyclopedia

Na = (6.022045±0.000031)*10 23 the number of molecules in a mole of any substance or the number of atoms in a mole simple substance. One of the fundamental constants, with the help of which you can determine quantities such as, for example, the mass of an atom or molecule (see... ... Collier's Encyclopedia

From school course In chemistry, we know that if we take one mole of any 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 this form: 6.02. 10^23.

However, why is Avogadro’s constant (in Ukrainian “became Avogadro”) equal to exactly this value? There is no answer to this question in textbooks, and historians of chemistry offer the most different versions. It seems that Avogadro's number has a certain secret meaning. After all, there are magic numbers, which some include pi, Fibonacci numbers, seven (in the east eight), 13, etc. We will fight the information vacuum. We will not talk about who Amedeo Avogadro is, and why a crater on the Moon was also named in honor of this scientist, in addition to the law he formulated and the constant he found. Many articles have already been written about this.

To be precise, I was not involved in counting molecules or atoms in any specific volume. The first who tried to find out how many molecules of gas

contained in a given volume at the same pressure and temperature, was Joseph Loschmidt, and this was in 1865. As a result of his experiments, Loschmidt came to the conclusion that in one cubic centimeter any gas in normal conditions is 2.68675 . 10^19 molecules.

Subsequently, independent methods were invented on how to determine Avogadro's number, and since the results mostly coincided, this once again spoke in favor of the actual existence of molecules. On this moment the number of methods exceeded 60, but in last years scientists are trying to further improve the accuracy of the estimate to introduce a new definition of the term “kilogram”. So far, the kilogram has been compared to a chosen material standard without any fundamental definition.

However, let's return to our question - why this constant is equal to 6.022. 10^23?

In chemistry, in 1973, for convenience in calculations, it was proposed to introduce such a concept as “amount of substance”. The mole became the basic unit for measuring quantity. According to IUPAC recommendations, the amount of any substance is proportional to the number of its specific elementary particles. The proportionality coefficient 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 a.u.m. corresponds to one twelfth of the mass of one carbon atom 12C and is 1.66053878.10^(−24) grams. If you multiply 1 amu. by Avogadro's constant, we get 1.000 g/mol. Now let's take some, say, beryllium. According to the table, the mass of one beryllium atom is 9.01 amu. Let's calculate what one mole of atoms of this element is equal to:

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

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

Avogadro's constant was specially chosen so that the molar mass corresponded to an atomic or dimensionless quantity - relative molecular. We can say that Avogadro's number owes its appearance, on the one hand, to the atomic unit of mass, and on the other, to the generally accepted unit for comparing mass - the gram.

N A = 6.022 141 79(30)×10 23 mol −1.

Avogadro's law

At the dawn of the development of atomic theory (), A. Avogadro put forward a hypothesis according to which, at the same temperature and pressure, equal volumes of ideal gases contain the same number of molecules. This hypothesis was later shown to be a necessary consequence of the kinetic theory, and is now known as Avogadro's law. It can be formulated as follows: one mole of any gas at the same temperature and pressure occupies the same volume, under normal conditions equal 22,41383 . This quantity is known as the molar volume of a gas.

Avogadro himself did not estimate the number of molecules in a given volume, but he understood that this was a very large value. The first attempt to find the number of molecules occupying a given volume was made by J. Loschmidt; it was found that 1 cm³ of an ideal gas under normal conditions contains 2.68675·10 19 molecules. After the name of this scientist, the indicated value was called the Loschmidt number (or constant). Since then, a large number of independent methods for determining Avogadro's number have been developed. The excellent agreement between the obtained values ​​is convincing evidence of the real existence of the molecules.

Relationship between constants

• Through the product of Boltzmann's constant, the Universal Gas Constant, R=kN A.
• Faraday's constant is expressed through the product of the elementary electric charge and Avogadro's number, F=eN A.

see also

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See what "Avogadro's Constant" is in other dictionaries:

Avogadro's constant- Avogadro konstanta statusas T sritis Standartizacija ir metrologija apibrėžtis Apibrėžtį žr. Priede. priedas(ai) Grafinis formatas atitikmenys: engl. Avogadro constant vok. Avogadro Constante, f; Avogadrosche Konstante, f rus. Avogadro's constant... Penkiakalbis aiškinamasis metrologijos terminų žodynas

Avogadro's constant- Avogadro konstanta statusas T sritis fizika atitikmenys: engl. Avogadro's constant; Avogadro's number vok. Avogadro Constante, f; Avogadrosche Konstante, f rus. Avogadro's constant, f; Avogadro's number, n pranc. constante d'Avogadro, f; nombre… … Fizikos terminų žodynas

Avogadro's constant- Avogadro konstanta statusas T sritis Energetika apibrėžtis Apibrėžtį žr. Priede. priedas(ai) MS Word formatas atitikmenys: engl. Avogadro's constant vok. Avogadro Constante, f; Avogadrosche Konstante, f rus. Avogadro's constant, f; constant... ... Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas

- (Avogadro number) (NA), the number of molecules or atoms in 1 mole of a substance; NA=6.022?1023 mol 1. Named after A. Avogadro... Modern encyclopedia

Avogadro's constant- (Avogadro number) (NA), the number of molecules or atoms in 1 mole of a substance; NA=6.022´1023 mol 1. Named after A. Avogadro. ... Illustrated Encyclopedic Dictionary

Avogadro Amedeo (9.8.1776, Turin, ‒ 9.7.1856, ibid.), Italian physicist and chemist. Received legal education, then studied physics and mathematics. Corresponding member (1804), ordinary academician (1819), and then director of the department... ...

- (Avogadro) Amedeo (9.8.1776, Turin, 9.7.1856, ibid.), Italian physicist and chemist. He received a law degree, then studied physics and mathematics. Corresponding member (1804), ordinary academician (1819), and then director of the physics department... ... Great Soviet Encyclopedia

Constant fine structure, usually denoted as, is a fundamental physical constant that characterizes the strength of electromagnetic interaction. It was introduced in 1916 by the German physicist Arnold Sommerfeld as a measure... ... Wikipedia

- (Avogadro’s number), the number of structural elements (atoms, molecules, ions or others) in units. number of va in va (in one pier). Named in honor of A. Avogadro, designated NA. A.p. is one of the fundamental physical constants, essential for determining the multiplicity ... Physical encyclopedia

CONSTANT- a quantity that has a constant value in the area of ​​its use; (1) P. Avogadro is the same as Avogadro (see); (2) P. Boltzmann universal thermodynamic quantity relating energy elementary particle with her temperature; denoted by k,… … Big Polytechnic Encyclopedia

Books

• Biographies of physical constants. Fascinating stories about universal physical constants. Issue 46
• Biographies of physical constants. Fascinating stories about universal physical constants, O. P. Spiridonov. This book is devoted to the consideration of universal physical constants and their important role in the development of physics. The purpose of the book is to tell in a popular form about the appearance in the history of physics...

Quantity of substanceν is equal to the ratio of the number of molecules in a given body to the number of atoms in 0.012 kg of carbon, that is, the number of molecules in 1 mole of a substance.
ν = N / N A
where N is the number of molecules in a given body, N A is the number of molecules in 1 mole of the substance of which the body consists. N A is Avogadro's constant. The amount of a substance is measured in moles. Avogadro's constant is the number of molecules or atoms in 1 mole of a substance. This constant was named after the Italian chemist and physicist Amedeo Avogadro(1776 – 1856). 1 mole of any substance contains the same number of particles.
N A = 6.02 * 10 23 mol -1 Molar mass is the mass of a substance taken in the amount of one mole:
μ = m 0 * N A
where m 0 is the mass of the molecule. Molar mass is expressed in kilograms per mole (kg/mol = kg*mol -1). Molar mass is related to relative molecular mass by:

μ = 10 -3 * M r [kg*mol -1 ]
The mass of any quantity of substance m is equal to the product of the mass of one molecule m 0 by the number of molecules:
m = m 0 N = m 0 N A ν = μν
The amount of a substance is equal to the ratio of the mass of the substance to its molar mass:

ν = m/μ
The mass of one molecule of a substance can be found if the molar mass and Avogadro's constant are known:
m 0 = m / N = m / νN A = μ / N A

Ideal gas - mathematical model gas, in which it is assumed that potential energy the interactions of molecules can be neglected compared to their kinetic energy. There are no forces of attraction or repulsion between molecules, collisions of particles with each other and with the walls of the vessel are absolutely elastic, and the interaction time between molecules is negligible compared to the average time between collisions. In the extended model of an ideal gas, the particles of which it consists also have a shape in the form of elastic spheres or ellipsoids, which makes it possible to take into account the energy of not only translational, but also rotational-oscillatory motion, as well as not only central, but also non-central collisions of particles, etc. . )