2019-03-29 11:11:19
Matter is made up of atoms, that was already proposed by the wise Democritus 2,400 years ago, but his proposal seemed too far-fetched to be accepted unreservedly, that is why he slept the sleep of the just until in the century XIX, an Englishman named John Dalton, recovered it. For Dalton, matter is discontinuous, that is, it is made up of differentiated and indivisible particles. Now we know that this is not the case, that atoms are composed, in turn, of smaller particles, but Dalton’s proposal went much further than that of Democritus by ensuring that there were substances, “elements”, whose atoms were all the same. from each other but different from those of another elemental substance. Thus, for him, two different elementary substances were made up of atoms that differed from each other in their mass and properties. The atoms of different elements can be combined with each other, forming larger groups called molecules, which allow us to obtain the immense variety of substances that exist in Nature.
These concepts, which are obvious to us, laid the foundations for understanding the essence of matter and its arrangement from its different atoms. If Democritus and Dalton’s proposal was correct, there must be many kinds of atoms, as many as elements, but how many? Now a total of 118 are known and we are used to representing them in an exquisitely ordered way in what is known as the Periodic Table, the basis of which was proposed in 1869, 150 years ago, by the Russian chemist Dmitri Ivanovich Mendeleev.
Arriving at that arrangement and, above all, at knowing the chemical and physical properties of each of the elements that appear in the Periodic Table, has been one of the greatest odysseys written by humanity. Our guest on Talking to Scientists, Fernando Carrillo-Hermosilla, professor of inorganic chemistry at the Faculty of Chemical Sciences and Technologies of Ciudad Real, invites us on a walk through the history of chemistry with the Periodic Table in the background of his story. It is an exciting journey that we developed in two consecutive Talking with Scientists programs.
Today we will learn about some of the historical facts that shaped the knowledge of chemical elements and their properties. Fernando explains how the search for the basic constituents of matter starts from the oldest philosophies, philosophies that attributed the origin of all things to just four elements, namely earth, water, air and fire, an idea that was kept alive well into the Middle Ages. Parallel to this philosophical conception, alchemists handled other elements, some known from the most remote antiquity, such as gold, silver, iron or copper. These substances can be found in their purest form in nature and have been used since ancient times to make utensils, ornaments and, above all, weapons. It was that technology that ushered in the prehistoric ages, such as the “Copper Age” or the “Iron Age”. To those initial elements, the alchemists, who were the predecessors of today’s chemists, in their search for the “Philosopher’s Stone” added new discoveries.
When Mendeleyev proposed his periodic table, 63 different elements were known. An elementary way of ordering them was based on their atomic weight, a measure of the mass of each of the atoms referenced to the lightest of them, which was identified as hydrogen. Sorting according to increasing atomic weights doesn’t require much effort, but there was something else. What really caught the attention of those chemists was that certain physical and chemical properties seemed to repeat themselves following specific periods. These periodicities served as the basis for Mendeleev to create a special arrangement, in the form of rows and columns, which offered additional information on the chemical and physical properties of the different elements. The most impressive thing about that table was that, in addition to ordering the known elements, it left empty places that, according to him, should be occupied by elements not yet discovered. That was the great success of Mendeleev, the predictive power of the Periodic Table from him. Later, gallium, scandium and germanium were discovered, the elements that occupied the places predicted by the Russian chemist.
We have given here only a few brushstrokes about the content of the interview, an interview that ends today with stories about the discovery of the elements of the periodic table, three of which, Platinum, Vanadium and Tungsten, had researchers as protagonists linked to Spain and Latin America, although the details of those discoveries will be revealed in the next chapter of Talking to Scientists.
I invite you to listen to Fernando Carrillo-Hermosilla, professor of inorganic chemistry at the Faculty of Chemical Sciences and Technologies of Ciudad Real, University of Castilla la Mancha. Twitter: @IYPT_UCLM2019
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