Introduction
The discovery of the periodic table of chemical elements has become one of the milestones in the history of development of chemistry as a science. The pioneer of the table was Russian scientist Dmitri Mendeleev. Extraordinary person with a broad scientific outlook managed to combine all of ideas about the nature of the chemical elements into a single coherent concept.
In the distant 1668, prominent Irish chemist, physicist and theologian Robert Boyle published a book, which has debunked many myths about alchemy, in which he talked about the indecomposable chemical elements. The scientist also brought a list consisting of only 15 elements, but thought that there might be more elements. This was the starting point not only in finding new elements, but in their systematization.
A hundred years later, French chemist Antoine Lavoisier gave the new list, which included 35 elements. 23 of them were later recognized as indecomposable.
In 1808, John Dalton proposed a new classification of chemical elements, where they were all linearly ordered by increasing atomic weight.
A huge contribution to the development of the chemical atomic in and the solution to the problem of atomic weights was introduced by the Swedish chemist Jöns Jakob Berzelius. From 1807 he began a systematic study of the elemental composition of compounds, presenting a huge amount of evidence in favor of the law of constant composition. In 1814, Berzelius published the first table of atomic weights, in which the atomic weight of 41 elements were given (for compiling the table, Berzelius needed to determine the composition of almost 2 000 connections!)
The search for new elements was carried out by chemists all over the world and all they progressed quite well. A crucial role in this issue was played by a Russian chemist Dmitri Mendeleev: he came up with the idea of the possibility of the existence of the relationship between the atomic mass of the elements and their place in the "hierarchy".
Comparing between known chemical elements, in the end, after enormous work, Mendeleyev found that dependence, a common regular connection between the individual elements in which they appear as a unified whole, where each element’s properties are not something self-existing, but a properly and periodically recurring phenomenon.
So, in February 1869 the periodic law of Mendeleev was formulated. In the same year, on March 6, the report prepared by D. I. Mendeleev, under the title "Correlation of properties with atomic weight of elements" was presented by N. Menshutkin at the meeting of the Russian chemical society.
In the same year, a publication appeared in the German journal "Zeitschrift für Chemie", and in 1871 the journal "Annalen der Chemie" published a large publication of D. Mendeleev devoted his opening — "Die periodische Gesetzmässigkeit der Elemente" (Periodic regularity of the chemical elements).
The creation of the periodic table
Although, the idea came to Mendeleev in a fairly short period of time, he could not make his conclusions for a long time. It was important for him to present his idea in the form of clear generalizations, a strict and clear system.
According to biographers, after this conversation, the scientist had been working on creating a table for three days and three nights, even without rest. He went over various options which could combine elements to the table. The work was complicated by the fact that at the time of the creation of the periodic system, not all chemical elements that are present there today were known to science.
Many have heard the story of Mendeleev that his table was a dream. This version was actively spread by the above-mentioned colleague of Mendeleev, A. Inostrantsev as a funny story, which he used to entertain his students. He said that Mendeleev went to sleep and saw the table in a dream in which all the chemical elements were arranged in the correct order. After that, the students even joked that the same method was used to discover 40° vodka.
In 1869-1871, Mendeleev continued to develop the extended and accepted by the scientific community idea of periodicity. One of these steps was the introduction of the concept of the place of the element in the periodic system as a totality of its properties in comparison with properties of other elements.
Based on this and based on the results obtained during the study of the progression of the glassforming oxides, Mendeleev corrected the atomic masses of the 9 elements, including beryllium, indium, uranium and others.
While working, Mendeleev sought to fill the empty cells in the table. As a result, in 1870, he had predicted the discovery of the elements, unknown at that time to the science. Mendeleyev figured out the atomic weights and described the properties of three yet undiscovered elements:
" ekaaluminium " - opened in 1875 and named gallium,
" ekaboron " - opened in 1879 and named scandium,
" ekasilicon " - opened in 1885, named germanium.
Following his forecasts, eight more elements were opened, including polonium (opened in 1898), astatine (opened in 1942-1943), technetium (opened in 1937), rhenium (opened in 1925) and francium (opened in 1939).
In 1900, Dmitri Mendeleev and William Ramsay came to the conclusion about the necessity of inclusion of elements particular, the zero group in the periodic system. Today, these elements are called noble gases (up to 1962 these gases were called inert).
The organizing principle of the periodic system
In his table, Mendeleev arranged the chemical elements in rows in ascending order of their weight, picking up the length of the rows so that chemical elements in a column have similar chemical properties.
Experimental determination of the charges of the nuclei, carried out by G. Moseley in 1914, a vindication of D. Mendeleev’s thoughts, in which he gave preference to chemical properties rather than atomic weights of elements when determining their final location in the periodic table.
Noble gases - helium, neon, argon, krypton, xenon and radon are reluctant to react with other elements and exhibit low chemical activity and therefore are in the far right column.
In contrast, the elements of the left column, lithium, sodium, potassium and other react with other substances violently, the process is explosive. Elements in the other columns of the table are behaving similarly - inside the column, these properties are similar, but vary from one column to another.
Periodic system in the first embodiment only reflected an existing state of affairs in the nature. Original table did not explain why this should be so. And only with the advent of quantum mechanics, it became clear the true meaning of the elements in the periodic table.
Chemical elements up to uranium (92 protons and 92 electrons) occur in nature. Starting with the number 93, that are artificial elements created in the laboratory.
