The nineteenth century in the history of mankind is the century in which many sciences were reformed, including chemistry. It was at this time that Mendeleev's periodic system appeared, and with it the periodic law. It was he who became the basis of modern chemistry. The periodic system of D. I. Mendeleev is a systematization of elements, which establishes the dependence of chemical and physical properties on the structure and charge of an atom of a substance.
History
The beginning of Mendeleev's periodic system was laid by the book "The ratio of properties with the atomic weight of elements", written in the third quarter of the 17th century. It displayed the basic concepts of relatively known chemical elements (at that time there were only 63 of them). In addition, for many of them, the atomic masses were determined incorrectly. This greatly interfered with the discovery of D. I. Mendeleev.
Dmitry Ivanovich started his work by comparing the properties of elements. First of all, he took up chlorine and potassium, and only then moved on to work with alkali metals. Armed with special cards on which chemical elements were depicted, he repeatedlyI tried to assemble this “mosaic”: I laid it out on my desk in search of the necessary combinations and matches.
After much effort, Dmitry Ivanovich nevertheless found the pattern he was looking for, and lined up the elements in periodic series. Having received empty cells between the elements as a result, the scientist realized that not all chemical elements were known to Russian researchers, and that it was he who should give this world the knowledge in the field of chemistry that had not yet been given by his predecessors.
Everyone knows the myth that the periodic table appeared to Mendeleev in a dream, and he collected the elements from memory into a single system. This is, roughly speaking, a lie. The fact is that Dmitry Ivanovich worked on his work for quite a long time and with concentration, and it exhausted him greatly. While working on the system of elements, Mendeleev once fell asleep. When he woke up, he realized that he had not finished the table, and rather continued filling in the empty cells. An acquaintance of his, a certain Inostrantsev, a university teacher, decided that Mendeleev's table was a dream and spread this rumor among his students. This is how this hypothesis appeared.
Fame
The periodic table of chemical elements of Mendeleev is a reflection of the periodic law created by Dmitry Ivanovich in the third quarter of the 19th century (1869). It was in 1869 at a meeting of the Russian chemical community that Mendeleev's notification about the creation of a certain structure was read out. And in the same year, the book "Fundamentals of Chemistry" was published, in whichMendeleev's periodic table of chemical elements was published for the first time. And in the book "The natural system of elements and its use to indicate the qualities of undiscovered elements", D. I. Mendeleev first mentioned the concept of "periodic law".
Structure and placement rules
The first steps in creating the periodic law were made by Dmitry Ivanovich back in 1869-1871, at that time he worked hard to establish the dependence of the properties of these elements on the mass of their atom. The modern version is a two-dimensional table of elements.
The position of an element in the table has a certain chemical and physical meaning. By the location of the element in the table, you can find out what its valency is, determine the number of electrons and other chemical features. Dmitry Ivanovich tried to establish a connection between elements, both similar in properties and different.
He put valency and atomic mass as the basis for the classification of chemical elements known at that time. Comparing the relative properties of elements, Mendeleev tried to find a pattern that would unite all known chemical elements into one system. By arranging them based on the increase in atomic masses, he still achieved periodicity in each of the rows.
Further development of the system
The periodic table, which appeared in 1969, has been refined more than once. With the adventnoble gases in the 1930s, it was possible to reveal the newest dependence of the elements - not on mass, but on the serial number. Later, it was possible to establish the number of protons in atomic nuclei, and it turned out that it coincides with the serial number of the element. Scientists of the 20th century studied the electronic structure of the atom. It turned out that it also affects the frequency. This greatly changed the idea of the properties of elements. This point was reflected in later editions of Mendeleev's periodic system. Each new discovery of the properties and features of the elements fit organically into the table.
Characteristics of the periodic system of Mendeleev
The periodic table is divided into periods (7 rows arranged horizontally), which, in turn, are divided into large and small. The period begins with an alkali metal and ends with an element with non-metallic properties.
Dmitry Ivanovich's table is vertically divided into groups (8 columns). Each of them in the periodic system consists of two subgroups, namely, the main and secondary. After long disputes, at the suggestion of D. I. Mendeleev and his colleague W. Ramsay, it was decided to introduce the so-called zero group. It includes inert gases (neon, helium, argon, radon, xenon, krypton). In 1911, scientists F. Soddy proposed to place indistinguishable elements, the so-called isotopes, in the periodic system - separate cells were allocated for them.
Despite the fidelity and accuracy of the periodic system, the scientific community for a long time did not want to recognizethis discovery. Many great scientists ridiculed the activities of D. I. Mendeleev and believed that it was impossible to predict the properties of an element that had not yet been discovered. But after the alleged chemical elements were discovered (and these were, for example, scandium, gallium and germanium), Mendeleev's system and his periodic law became the theoretical basis of the science of chemistry.
Table in modern times
Mendeleev's Periodic Table of Elements is the basis of most chemical and physical discoveries related to atomic and molecular science. The modern concept of the element has developed precisely thanks to the great scientist. The advent of Mendeleev's periodic system has made fundamental changes in the ideas about various compounds and simple substances. The creation of a periodic system by a scientist had a huge impact on the development of chemistry and all sciences related to it.
