EducationSecondary education and schools

Periodic system of Mendeleev. Chemical elements of the periodic table

The nineteenth century in the history of mankind is the century in which many sciences have been reformed, including chemistry. It was at this time that Mendeleyev's periodic system appeared, and with it a periodic law. It was he who became the basis of modern chemistry. Periodic system of DI Mendeleyev is the systematization of elements, which establishes the dependence of chemical and physical properties on the structure and charge of the atom of matter.

History

The beginning of Mendeleyev's periodic system was laid down in the book "The ratio of properties to the atomic weight of elements," written in the third quarter of the 17th century. It showed the basic concepts of known chemical elements (at the time there were only 63 of them). In addition, many of them atomic masses were identified incorrectly. This greatly hampered the discovery of DI Mendeleyev.

Dmitry Ivanovich began his work by comparing the properties of elements. First of all, he took up chlorine and potassium, and then went to work with alkali metals. Armed with special cards on which chemical elements were depicted, he repeatedly tried to collect this "mosaic": he laid out on his desk in search of the necessary combinations and coincidences.

After much effort, Dmitry Ivanovich still found the pattern he was looking for, and built the elements into periodic series. Having received as a result empty cells between elements, the scientist realized that not all chemical elements are known to Russian researchers, and that he should give this world knowledge in the field of chemistry that has not yet been given by his predecessors.

Everyone knows the myth that Mendeleev's periodic table appeared in a dream, and he collected the elements from memory in a single system. This, roughly speaking, is a lie. The fact is that Dmitry Ivanovich worked for a long time and concentrated on his work, and it was very exhausting. 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. His acquaintance, a certain Foreigner, a university teacher, decided that Mendeleev's table had a dream and spread this rumor among his students. So this hypothesis appeared.

Fame

Periodic system of chemical elements Mendeleyev is a reflection of the periodic law created by Dmitry Ivanovich in the third quarter of the XIX century (1869). It was in 1869 at a meeting of the Russian chemical community that Mendeleyev's notice was read of creating a certain structure for him. And in the same year the book "Fundamentals of Chemistry" was published, in which the periodic system of chemical elements of Mendeleyev was first published. And in the book "The Natural System of Elements and Its Use to Indicate the Qualities of Unrevealed Elements" DI Mendeleev first mentioned the concept of "periodic law".

Structure and rules of placement of elements

The first steps in the creation of the periodic law were made by Dmitry Ivanovich back in 1869-1871, while he was working hard to establish the dependence of the properties of these elements on the mass of their atoms. The modern version is a two-dimensional table.

The position of the 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 is its valence, determine the number of electrons and other chemical features. Dmitry Ivanovich tried to establish a connection between the elements, which are similar to each other in terms of properties, as well as different.

Based on the classification of chemical elements known at that time, he put the valence and atomic mass. Comparing the relative properties of the elements, Mendeleev tried to find a regularity that would unite all the known chemical elements into one system. Having arranged them, based on the increase in atomic masses, he nevertheless achieved periodicity in each of the series.

Further development of the system

The periodic table that appeared in 1969 was repeatedly elaborated. With the advent of noble gases in the 1930s, it turned out to reveal the newest dependence of the elements - not on the mass, but on the ordinal 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 XX century studied the electronic structure of the atom. It turned out that it also affects the periodicity. This greatly changed the idea of the properties of the elements. This point was reflected in the later editions of the periodic system of Mendeleyev. Each new discovery of the properties and features of the elements fit organically into the table.

Characteristics of the Periodic Table of Mendeleev

The periodic table is divided into periods (7 lines horizontally), which, in turn, are divided into large and small. The period begins with an alkali metal, and ends with an element with nonmetallic properties.
Vertically, the table of Dmitry Ivanovich is divided into groups (8 columns). Each of them in the periodic system consists of two subgroups, namely, the main and secondary. After much debate on the proposal of DI Mendeleyev and his colleague U. Ramsay it was decided to introduce the so-called zero group. It includes inert gases (neon, helium, argon, radon, xenon, krypton). In 1911, the scientist F. Soddy was invited to put in the periodic system and indistinguishable elements, the so-called isotopes - for them were isolated cells.

Despite the fidelity and accuracy of the periodic system, the scientific community for a long time did not want to recognize this discovery. Many great scientists ridiculed the activities of DI Mendeleyev 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), the Mendeleev system and its periodic law became the theoretical basis of the science of chemistry.

Table in modern times

The periodic system of Mendeleev's elements is the basis of most of the chemical and physical discoveries associated with atomic-molecular theory. The modern concept of the element has developed precisely thanks to the great scientist. The appearance of the periodic system of Mendeleev brought about cardinal changes in the notion of various compounds and simple substances. The creation of a periodic system by scientists had a tremendous impact on the development of chemistry and all sciences adjacent to it.

Similar articles

 

 

 

 

Trending Now

 

 

 

 

Newest

Copyright © 2018 en.birmiss.com. Theme powered by WordPress.