What is Avogadro’s number?

Avogadro’s number

The Avogadro number is a constant used in the field of analytical chemistry to quantify the number of particles or microscopic entities from macroscopic measures like mass. It is very important to know this number to understand the composition of molecules, their interactions and combinations. For example, to create a water molecule it is necessary to combine two hydrogen atoms and one oxygen atoms to obtain one mole of water. Avogadro’s number is a constant that must be multiplied by the number of atoms of each element to obtain the value of oxygen (6.023 x 10 23 atoms of O) and Hydrogen (2x 6.022x 10 23 ) that form one mole of H 2 O

Avogadro's number

  • Value:  6,023 x 10 23
  • Symbol:  Na or L
  • Formula:  Na = F / e

What is Avogadro’s number?

Avogadro’s number is a constant that represents the number of atoms in twelve grams of pure 12-carbon . This figure makes it possible to count microscopic entities. This comprises the number of elementary entities (that is, of atoms, electrons, ions, molecules) that exist in a mole of any substance. Avogadro’s number is equal to (6.022 x 10 raised to 23 particles) and is symbolized in the formulas with the letters L or NA. In addition, it is used to make conversions between grams and atomic mass unit . The unit of measurement for Avogadro’s number is the mole (mol-1) but it can also be defined in pound-mol (lb / mol-1) and in ounce-mol (oz / mol-1).

  • What is Avogadro’s number
  • What does Avogadro’s number represent?
  • How Avogadro’s number is calculated
  • History

What is Avogadro’s number

Avogadro’s number is 602,000,000,000,000,000,000,000 which is equal to 602,000 trillion = 6.02 x 10 23 . This value is found from the number of carbon atoms contained in 12 grams of carbon 12 raised to the power of 23.

It is important to mention that depending on the unit of measurement used, the number may vary . In this sense, if we work with mol, the number is 6.022140857 (74) x 10 23 mol -1 .

If you work with pounds it  will be 2,731 597 34 (12) × 10 26  (Lb-mol) -1 .

If you work with ounces, it  will be 1.707 248434 (77) x 10 25 (oz-mol) -1 .

What does Avogadro’s number represent?

Avogadro’s number represents the number of atoms that exist in twelve grams of carbon-12 .

This number represents a quantity without an associated physical dimension , so it is considered a pure number that allows describing a physical characteristic without an explicit dimension or unit of expression. For that reason, it has the numerical value of a constant that the units of measure have.

How Avogadro’s number is calculated

Avogadro’s number can be calculated by measuring the Faraday constant (F) that represents the electric charge carried by one mole of electrons and dividing it by the elemental charge (e). This formula is a = F / e

Avogadro’s constant can be calculated thanks to analytical chemistry techniques known as coulombimetry , which determine the amount of matter transformed during the electrolysis reaction by measuring the amount of matter consumed or produced in coulombs.

There are also other methods to calculate it such as the electron mass method, known as CODATA or the crystal density measurement system using X-rays.


Avogadro’s number or Avogadro’s constant has this name in honor of the Italian scientist Amedeo Avogadro who in 1811 determined that the volume of a gas at a given pressure and temperature is proportional to the number of atoms or molecules regardless of the nature of the gas. gas.

In 1909, Jean Perrin , a French physicist – winner of the Nobel Prize in Physics in 1926 – proposed to name the constant in honor of Avogadro . Perrin through various methods verified the use of the Avogadro constant and its validity in many of his works.

Initially, it was called Avogadro’s number to refer to the number of molecule-grams of oxygen, but in 1865, the scientist Johann Josef Loschmidf  called Avogadro’s number, Avogadro’s constant . Loschmidf estimated the mean diameter of air molecules by a method equivalent to calculating the number of particles in a specific volume of gas. For this reason, the value of the particle density of an ideal gas is known as Loschmidt’s constant, which is approximately proportional to Avogadro’s constant. From that moment on, the symbol for Avogadro’s number or Avogadro’s constant can be NA (Avogadro’s number) or L (in honor of Loschmid).

A curious fact about the history of Avogadro’s number is that the Italian scientist Amedeo Avogadro in life never measured the volume of any particle because in his time there were not the necessary elements to be able to do it, but it is thanks to his contributions that Perrin developed this constant and that is why he gave it that name.

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