What is Avogadro's constant

To study the chemical nature of matter, science relies on the establishment of many constants. Constants are fixed values ​​of a certain magnitude, which normally allow us to have a proportionality between two magnitudes. Among the most commonly used constants is Avogadro's constant.

In this lesson from a TEACHER we will focus on studying what is Avogadro's constant, a number, value or a proportion factor that reveals the relationship between the typical mass (amount of matter) of a substance and the mass present in a test sample of the same.

Index

1. Definition of Avogadro's constant
2. What is Avogadro's constant for?
3. Who discovered Avogadro's number?

One of the basic pillars of all modern sciences is the international system of units or international metric system. This set of measurement units allows all of us to have a value as the same reference, which allows us to measure a certain magnitude. Imagine that, for each of us, a meter had a different length, it would be a real chaos!

The international system of units was invented and has been used for centuries, but today a change has been proposed. In ancient times, the values ​​of the different quantities were defined by materials or reference systems that could be seen and touched. At present there is a general agreement of change, so that the units are based on the fundamental constants of nature and in specific defined numbers and, therefore, constants that cannot change throughout the weather. One of them is the Avogadro's constant.

Avogadro's constant is currently defined as the number of atoms in 12 grams of carbon-12 and its approximate known value is 6.02214129 × 10²³. However, the exact number depends on the definition of a kilogram, which for the moment is defined as the mass of an arbitrary alloy bar. of platinum-iridium found in Paris (France), something that does not convince researchers since this value is known to vary over time.

Today, researchers such as Phil Fraundorf, from the University of Missouri-St Louis (USA) or those who form the Avogrado Project (formed by the Institutes Metrology Nationals of Europe, Australia, Japan, Russia and the United States), are proposing new methods to determine the reference value of the kilo according to a constant.

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Knowing what the Avograd constant is and knowing its value has allowed us to use it in physics and chemistry since its discovery. One of the main characteristics of the Avogadro number or constant is to have a value dimensionless, which provides a ratio or link value between a number of useful physical constants when moving between the atomic scale and the macroscopic scale.

For example, set the relationship Come in:

• the gas constant (R) and Boltzmann's constant (kB), measured in J mol⁻¹ K⁻¹: R = Na · kB
• the cFaraday's constant (F) and elemental charge (e), in C mol⁻¹: F = Na e

But, without a doubt, one of the greatest applications of Avogadro's constant is the definition or establishment of the atomic mass constant (mu) from knowledge of molar mass constant (Mu): mu = Mu / Na.

In addition, knowing what the Avogrado constant is and what its value is also serves establish a mass relationship between reactants and between reactants and products of chemical reactions. By writing the balanced reaction that describes any chemical process, we can know the number of moles involved in it. Thanks to this and to the knowledge of the atomic masses of the elements (and therefore, of the masses molecular), we are able to transform the value of the moles of reactants and products in their respective mass values.

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Avogadro's number was first introduced in the 19th century, specifically in 1811, from the hand of Amadeo Avogadro, an Italian scientist. This scientist showed for the first time that a volume of a gas at a specific pressure and temperature contains the same number of atoms or molecules, regardless of the nature of the gas itself.

The value of Avogadro's constant was first indicated, indirectly, by Johann Josef Loschmidt in 1865. Loschmidt estimated the mean diameter of molecules in air by a method equivalent to calculating the number of particles in a given volume of gas. This last value, the number density of particles in an ideal gas, is now named in his honor Loschmidt's constant. This constant is proportional to Avogadro's number and is related to Loschmidt because it is the root of the symbol L. In German literature they can sometimes refer to both constants with the same name, distinguishing them only by the units of measurement.

However the Avogadro's number itself was not postulated until 1909, when the French physicist Jean perrin, determined the exact value of Avogadro's constant using various experimental techniques and methods. This finding, which continues to be learned in colleges and universities around the world today, led to won the Nobel Prize in Physics in 1926 for the determination of Avogadro's constant by various methods different.

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