The periodic system of chemical elements became the first periodic table that collected all the chemical knowledge that mankind had by the second half of the 19th century. The article discusses in detail the question of when the periodic system of Mendeleev was discovered.
The famous Russian chemist
It is important to be aware of the scientific biography of our compatriot in order to understand when the periodic system of Mendeleev was discovered. So, the famous Russian chemist was born in Siberia in the city of Tobolsk on February 8, 1834. He graduated from the magistracy at the St. Petersburg Pedagogical Institute, and later was able to get the title of privat-docent. In 1859, D.I. Mendeleev went to Germany, namely to the University of Heidelberg in order to obtain a professorship. In 1865, he returned from Germany again to St. Petersburg and received the title of professor. In 1868, the scientist began work on the book "Fundamentals of Chemistry."
Scientific searches of Mendeleev
In the second half of the 19th century, humanity had already accumulated enough knowledge in chemistry, and this subject was taught as mandatory in all universities in Europe. However, information on chemical compounds and their properties was not collected and systematized, but was in a huge number of literary sources. As a result, the study of chemistry became a very slow, boring and inefficient task, because students had to spend hours searching for the necessary “crumbs” of knowledge in a whole mountain of literature. This situation greatly bothered D.I. Mendeleev.
After lengthy searches in literary sources, as well as performing his own chemical experiments in those cases when there was no information in the literature, Dmitry Ivanovich wrote a series of articles that made it possible to systematize and organize a huge amount of chemical knowledge. These works had a huge impact on the history of the development of chemistry, since they provided it with predictive power.
In his work, the scientist compared the chemical properties of various elements and found that they change regularly depending on their atomic mass. Unlike the German chemist Julius Lothar Meyer, Dmitry Ivanovich presented the results of his research in the form of a table, including elements with similar chemical properties in it.
The discovery of the periodic system of chemical elements
The table of the Russian chemist became the first published ordered table of chemical elements in the world. When was the periodic system of Mendeleev discovered? Many sources have a date - March 1869.
In the first table, the scientist included 63 chemical elements that were known in his time, placing them in order of increasing atomic weight. The masses of some elements stood with question marks, since the scientist did not fully trust the experiments in which these masses were established. Also, in the first table of D. I. Mendeleev there were empty cells, since the scientist himself believed that there could not be such a big difference in the atomic mass between neighboring elements and that there should be other elements that had yet to be discovered. Dmitry Ivanovich even predicted some properties of elements not yet discovered.
Chemical valency and batch properties
It is important not only when the periodic system of Mendeleev was discovered , but also the fact that the scientist discovered a correspondence between the sequence of arrangement of chemical elements in the table and their valency.
For example, sodium has a valency of 1 and can enter into a chemical compound with only one other atom, that is, the compound NaO 2 , in which sodium interacts with two oxygen atoms, is impossible. In turn, oxygen, whose valency is 2, can combine with two atoms of a single valency, which demonstrates the H 2 O compound. If oxygen reacts with an element that also has a valency of 2, then the reaction in atomic percent is in relation to 1 : 1, e.g. CaO. Nitrogen has a valency of 3, so for it the compound NH 3 is permissible and so on.
Thus, the relative positions that elements occupy in the chemical system of Mendeleev are related to their valencies.
The predictive power of the periodic law
The Russian scientist also established a periodic law (the reason why his table is called periodic), according to which the properties of chemical elements are a periodic function of their atomic weight.
The periodic table attracted the attention of famous chemists of the late 19th century only when the elements predicted by scientists were discovered and their properties were experimentally studied. As a result, it turned out that the theoretically established chemical properties of the elements in the empty cells of the table coincided with amazing accuracy with the properties of the newly discovered elements.
For example, Mendeleev in 1871 described the properties for an as yet unknown element, which was supposed to be next to silicon and have the same valency as he. After 15 years, this element was discovered by the German chemist Clemens Winkler and named Germany.
Noble gases and the periodic system of elements
The so-called noble gases were not known when Mendeleev published his table. However, after they were discovered, they once again confirmed the valency theory in the periodic table.
At the end of the 19th century, several chemical elements were discovered that could not be included in any of the groups of the periodic table. These elements were chemically inert, therefore they received the name of noble gases (argon, neon, xenon and others).
Their chemical inactivity was explained by the theory of valencies. The fact is that the valency of these elements is 0, so they are not able to react with others.
The inclusion of noble gases in the periodic table made DI Mendeleev’s periodic law more harmonious and complete.