Have you ever stopped to think about the immensity of the Universe that surrounds us? Far beyond what our eyes can see, on a microscopic scale, everything exists. a world of particles and molecules that give shape to everything we know, from the air we breathe to the objects we touch. What if we could count those tiny particles and quantify them? Well, although it may seem completely fanciful, it is not so and Avogadro’s number is a fundamental factor for this.
Represented by letters NTOhe Avogadro’s number It is the quantity that tells us how many particles there are in a mole of any substance, thus becoming one of the most important tools for understanding the world at a molecular level. And, although it is not one of the most famous figures of mathematics or physics – surely the golden ratio or the number pi sounds much more familiar to you – Avogadro’s constant is also positioned as a fundamental element without which, many branches of these disciplines would not even exist.
WHAT IS AVOGADRO’S NUMBER?
Thus, Avogadro’s constant is a magnitude that provides an important connection between mass and the number of particles in a substance. In technical language, it is defined as the number of constituent particles, whether atoms or molecules, which are found in a mole – a mole of a substance is its atomic mass in grams – of any substance; but in simpler terms, we can say that Avogadro’s number tells us how many particles there is in a specific quantity, regardless of its type or nature.
Currently, the accepted value for Avogadro’s constant is 6.02214087(62)x1023 – that is to say, six hundred two thousand two hundred fourteen trillion seventy-six thousand billion particles, a figure much greater than the number of grains of sand on all the beaches on Earth. And be careful, because Avogadro’s number has no units. That is, it can technically be used to tell anything, just as if we were talking about a hundred or a dozen. However, it’s such a massive number that it’s really only practical for small things, like atoms or molecules.
THE CONSTANT NAILING
The first to realize this constancy of particles in certain quantities of substance was an Italian scientist named Amadeo Avogadro. This chemist was born in Turin in 1776, at a time when chemistry was beginning to separate itself from alchemy and become a modern science. In 1811 he formulated a hypothesis that reinforced this transformation: he stated that Equal volumes of gases, under the same conditions of temperature and pressure, contained the same number of molecules. That is, this implied that the molar mass of any substance must contain a fixed number of atoms or particles, regardless of their type.
As is often the case with all revolutionary ideas, Avogadro’s postulate was received with skepticism, negativity and confusion. Part of the controversy derived from the lack of distinction between atoms and molecules, since they were concepts that were still developing. On the other hand, Dalton’s atomic theory, contemporary to Avogadro’s proposal, focused on atoms as the fundamental units of matter and did not consider elements such as molecules composed of several atoms.
Amadeo Avogadro drawn by C. Sentier.
In fact, Avogadro did not see his theory accepted during his lifetime. It was only after his death, in 1856, and with the development of the kinetic theory of gases, that his hypothesis began to gain acceptance. Thus, over the years, technological advances and experimental methods allowed us to refine the determination of Avogadro’s constant, leading the scientific community to recognize its importance for physics and chemistry.
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A NOBEL FOR A NUMBER
Specifically, the recognition of the constant was such in the years after Avogadro’s death that it was the subject of a Nobel Prize in 1926. The honoree was the French physicist Jean Baptiste Perrinwho was awarded under the argument “for his work on the discontinuity of matter and especially for his discovery of the laws that govern the movement of particles in suspension, work that is directly related to Avogadro’s constant and his study of atoms and molecules”.
But this award was more than deserved: Perrin played a fundamental role in the exact definition and determination of Avogadro’s number, establishing the bases to relate the solar masses of substances with the quantities of particles present in them. His work was crucial in validating Avogadro’s proposal and assigning a number to his hypothetical constant. He even named the figure after the Italian scientist instead of his own, as a sign of tribute.
In addition to Perrin, other scientists over the years have contributed significantly to the determination and understanding of Avogadro’s constant, although not all of them managed to have the recognition of the French. However, the Nobel was a way of underlining the importance of this constant, somewhat more unknown, as one of the fundamental figures that guide the understanding of the world at a molecular level, paying tribute to the impact it has had on science and, intrinsically, on society in general.
