A “chemical element” is all the atoms in the universe that are of a particular type. The definition of this “type” has undergone many changes over the past hundreds of years, starting with the work of John Dalton, the author of the first modern atomic theory, who reconciled the concepts of “atom” and “element” used in ancient Greek philosophy (by the way, in a number of European languages, the word elementalso translated as “element”). As you know, in the original formulation of the Periodic Law of Mendeleev, atomic weight appears, which, in the opinion of the great scientist, determined the periodic changes in the properties of elements. As of today in the Periodic Law, the property that determines which element an atom belongs to is the charge of its nucleus (equivalent to the number of protons in the nucleus). For example, if we have an atom with one proton in the nucleus, it is always hydrogen: this correspondence is unique and works both ways.
Modern versions of the Periodic Table are organized in such a way that the elements are arranged in order of increasing nuclear charge, which is more fundamental. An interesting point in the history of chemistry is that Mendeleev, of course, did not imagine that the atom has a positively charged nucleus, because he worked before the corresponding experiments of Rutherford, but intuitively arranged some of the elements out of order of increasing atomic weight (although this was its main criterion), but in the order of changes in the chemical properties of compounds with the participation of atoms of these elements. As a result, this approach was justified: when the new criterion for organizing elements became generally accepted, these cells remained in their places. Moreover, all the elements predicted by Mendeleev, which should have been located in the cells of the table that were “empty” at that time,
There are two versions of the Periodic Table most commonly used. In both cases, it is a rectangular table of cells of the same size arranged in rows (called periods) and columns (called groups). In the short period table, the d-elements are arranged in two rows, while in the long period table they are arranged in one row per period. It is the long-period version recommended by IUPAC (International Union of Pure and Applied Chemistry – the body that determines the entire chemical nomenclature). This display standard is accepted all over the world, but for some reason our schools never get used to it: the short period version of the table is still widely used in Russian education.
Due to the fact that such a display of a set of elements is most common, everyone usually visualizes the concept of a “chemical element” in this way, imagining some kind of finite-size table. In fact, it doesn’t have to be like that at all. There is no strict quantum-mechanical limit on how big an atom can be and what charge its nucleus can have, so there are no restrictions on the dimension of the table either. Theoretically, the series of elements can be continued indefinitely, but the word “theoretically” is, of course, the key here: scientific research is driven not only by interest in the world around us, but also by common sense.
A parallel and no less interesting question is: “How many more elements can we discover?” Here, many experimental restrictions arise: in terms of energy (very expensive accelerators are needed to detect superheavy elements), the detection limit (atoms of new elements are synthesized in the amount of tens or even units), the lifetime of certain isotopes (it can be the smallest fractions of a second), and so on. Further.
There are different ways to display the history of the discovery of new elements: for example, the last 300 years of scientific thought on this graph can be approximated by a straight line in nt coordinates. But when looking at this graph, it becomes obvious that the rate of discovery of chemical elements is decreasing (the straight line “bends”), and this is completely logical, since we have either discovered all the light and heavy elements on Earth or synthesized them. Only superheavy transuranium elements remain, the search for which is associated with all the problems that I outlined above (the probability of finding at least one stable isotope for these elements tends to zero). And a not quite scientific, but legitimate question arises: how expedient is this? The search for such elements is very interesting, but the practical application.
