Istituto Lombardo - Accademia di Scienze e Lettere - Incontri di Studio

SALUTO DEL PRESIDENTE DELL'ISTITUTO LOMBARDO

2019-10-13T17:37:46+02:00

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INTRODUZIONE

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TAVOLA PERIODICA, ELEMENTI E MINERALI: UNA STORIA AFFASCINANTE

2019-10-13T17:37:44+02:00

In the year 1869, 150 years ago, Dmitrij Ivanovič Mendeleev published the classification of the known chemical elements in the form of a periodic table. This scientific goal was achieved thanks to the genius both of Mendeleev, that had recognized the periodicity in the properties of the elements, and of those who had identified all the elements already known at Mendeleev’s time. This discovery process frequently occurred at the edge between chemistry and mineralogy, as a result both of the scientist’s curiosity and of the need to identify the minerals useful to the metals smelting. A brief description of the path that has lead to the discovery of all the elements of the periodic table is not possible; for that reason this work is going to deepen the analysis on the elements whose discovery has involved a mineral and was particularly peculiar. This discovery path had begun already in the ancient time. It is possible to say that the mankind started to isolate and handle the elements during the neolithic age, becoming, over time, more skillfull in recognizing new elements. The path has begun by using the metals already present in nature as native ores, as copper, silver and gold, all already known during the chalcolithic age. From this first step to the invention of the first extraction techniques and smelting, able to yield the metal starting from its minerals, it was a short step. In the ancient time at least nine elements were already known and used. We are talking about “elements”, giving to this word the meaning used in the modern chemistry. This last consideration could lead to another scenario that, however, is out of this speech: the evolution of the concept of “element”. The new elements discovery path, still before the modern definition of “element”, received a huge help by the alchemy: the isolation of four elements was achieved in that period. During the XVIII century the discovery of new elements has seen an acceleration, thanks to the historical context of the Age of Enlightenment. In that period two very similar stories involved the discovery of cobalt and nickel. Both these elements are named from creatures belonging to the miners’ mithology: the miners used to find frequently minerals that, based on their experience, should have contained metals. Those minerals, however, did not yield any known metal and, for this, the miners blamed fantasy creatures: the Kobolds, sprites stemming from Germanic mythology, and Nickel, a mischievous sprite also belonging to German miners mythology. These puzzles were solved by two scientist: George Brandt, that discovered the cobalt, and Axel Frederik Cronstedt, that discovered the nickel. A very peculiar case is represented by fluorine: between the demonstration, occurred in the 1771, that the fluorite contains a new element, and the isolation of elemental fluorine, successfully performed only in the 1886, more than one hundred years have passed. Sometimes the identification of new elements was the product of lucky coincidences. The beginning of the epopee of the rare earth elements discovery was one of these cases; it was determined by two main factors: the presence in Sweden of some important chemists and the discovery, at that time, of a strange mineral, called gadolinite, in a quarry close to the village of Ytterby. Sometimes the identification of a new element was determined by a very clever reasoning about incongruous data and measures. The fact that the radioactivity of the pitchblende (or uraninite) was too high considering only its content in uranium, has lead Marie Sklodowska Curie to the discovery of polonium. The discovery of new elements, in the last century, moved from the edge between chemistry and mineralogy to the edge between chemistry and physics.

MODELLO DELL'ATOMO, TEORIA QUANTISTICA E TAVOLA PERIODICA DEGLI ELEMENTI

2019-10-13T17:37:44+02:00

In this paper I attempt to sketch the path that brought from the Table of the Elements, essentially born in an chemical context, to its explanation in the framework of Atomic Physics.Thist involves the most advanced formalisms of Theoretical Physics, Quantum Mechanics and even Quantum Field Theory. I try to stress that the Table together with Spectroscopy has been among the main problems that have stimulated and even addressed the research in the latter frameworks.

TAVOLA PERIODICA SOTTO PRESSIONE: UNA PERIODICITA' DIVERSA ED UNA CHIMICA ESOTICA

2019-10-13T17:37:43+02:00

Our general and operative notion of chemistry, that enabling us to describe and interpret the structural, bonding and reactivity properties of the various compounds, is essentially rooted in the periodicity of properties of their constituting elements. Periodicity drove the path towards the proposition of the periodic table of elements and its rationalization thanks to the gradually acquired knowledge on the atomic electronic structure. Atomic radii periodicity mirrors the periodicity of the electronic configurations of the atoms’ outermost shell. The changes in atomic radii differentiate the chemical properties, hence the structures and properties of the elemental solids and of their compounds. Yet, under an external pressure, such a fully rationalized scenario may drastically change. When an atom is compressed, its average electron density increases and its outermost electronic shell is the easiest one to compress. At 100 Giga Pascal (GPa), that is at 10⁶ atmospheres, the change of the atomic radius along a period of the Periodic Table becomes much less evident and at 1000 GPa our classical notion of periodicity is completely lost. Under pressure, the energy due to the compression work made on a system adds up to its internal energy. With such an energy gain the system may reach regions of the potential energy surface which would not be otherwise accessible. The chemical bond nature may change, even radically, and new structures and bonding patterns, characterized by totally unexpected properties, become energetically stable and possible. For instance, sodium, which is a silvery-white, highly reactive metal, becomes a fully transparent insulator, while boron is turned into a partially ionic solid elemental phase because charge transfer takes place between differently clustered groups of boron atoms. The incredible chemical inertness of helium finally falls as it forms a stable compound with sodium, Na2He. Under a suitable pressure, compounds with unusual stoichiometry (Na₃Cl₂, Na₂Cl, Na₃Cl, NaCl₃, NaCl₇) may be observed, despite their formula would be immediately rejected if proposed by a student at any high-school or university exam, or new carbon allotropes may appear or the aromatic character of benzene may vanish. This new chemistry is usually predicted through ab-initio quantum mechanical methods and interpreted and rationalized with the most modern chemical bonding approaches. However, compounds anticipated in silico have then be reproduced experimentally in many cases, by using diamond anvil cells to synthesize them and a variety of in situ instrumental techniques to characterize them properly.

HOMO FABER: COME I METALLI HANNO SEGNATO E SEGNANO ANCHE OGGI LA CIVILTÀ DELL’UOMO

2019-10-13T17:37:42+02:00

The succession of various ages, from those of copper to that of bronze, then iron and so on, is dictated by the chemical properties of the various metals and, ultimately, by the periodic table of the elements. The capacity expressed by the homo faber to extract and work the different metals, have marked technological developments so radical as to be chosen by historians to designate real civilizations. Gold was the first metal used by man, although it could not be used either as a tool or as a weapon. More than any other ancient element, gold has always been associated with a timeless charm. None of the chemical elements discovered by modern science has been able to overcome its supremacy. Since the time of its discovery, gold has been used for ornamental purposes and only with technological development has it been used also for technical and scientific purposes. For titanium, however, the reverse path was verified, from its essentially technological use it then moved on to the artistic one. Starting in the 1960s, when titanium became available even for non-military uses, its applications have done nothing but grow and diversify. His artistic fame is unquestionably linked to the Guggenheim Museum in Bilbao designed by the architect Frank Gehry in 1997, while in Pedeferri’s titanochromies we have the combination of art and technology.

ORDINE DELLA NATURA E FIGURE DELLA VERITÀ

2019-10-13T17:37:41+02:00

The human knowledge and the order of nature: the problem of their relationship is the core of paper. The solution concerns the co-operation between the instrumental and technological knowledge and the sociale work of language.

CONCLUSIONI

2019-10-13T17:37:41+02:00

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