build an atomic-molecular theory in the 18-19 centuries.accompanied by an active increase in the number of known elements.Only in the first decade of the 19th century it was opened 14 new atoms.English chemist Humphry Davy became the champion among the "pioneers": in one year, he was using electrolysis 6 simple substances (Na, K, Mg, Ca, Sr, Ba).By 1830, it became known 55 chemical elements. existence of a large number of elements requiring their ordering and systematization.

history of the discovery of the periodic law

attempts to classify the chemical elements made before Mendeleev.Of these, the most significant were three works: the French chemist de Beguye Chancourtois, English chemist John Newlands and the German scholar
Julius Lothar Meyer.

In the works of these scholars have much in common.All they found the frequency of changing the properties of the elements according to their atomic weight, but could not create a single system, as many elements in their laws governing not find their place.No major conclusions from their observations, scientists do not succeed. First International Chemical Congress 1860 in Karlsruhe played a key role in identifying the frequency.

universal law, revealing the essence of relations between the atomic weights of elements, was discovered DIMendeleev in 1869.This law states that the elements exhibit a periodicity of properties, if you place them on the value of the atomic weight, and must expect the discovery of many more elements of similar properties with known substances, but having a larger atomic weight.

Periodic Table and its first published version

Draft periodic table appeared February 17 (March 1, New Style), 1869, and on March 1 has been published in a print version in the article "Experience of elements based on their atomic weight andchemical similarity. "March 6 Menshutkin professor made an official announcement about the discovery at a meeting of the Russian Chemical Society. In 1871 DIMendeleev published the textbook "Fundamentals of Chemistry".Periodic system was brought into it almost in its present form, with the periods and groups.

Guided open intervals, Mendeleev predicted the existence of new elements and even described their properties.So, they were described in detail the properties of then unknown elements identified by scientists as "eka-boron", "eka-aluminum" and "ekasilitsy."Later, these substances were experimentally obtained by other chemists (P. Lecoq de Buabodranom, L. Nilsson and K. Winkler), and outdoor Mendeleev periodic law was universally recognized.

explain the periodic law and justify the structure of the periodic system in the science of the 19th century it was impossible.Later, it was done with the help of quantum theory.And the properties of the elements, as well as the properties and forms of their compounds depends not so much on the atomic weight of many, to be more precise, on the charge of the nucleus of an atom, that is the atomic number of the element in the modern periodic table.