All elements usually presented in the chemistry of the periodic system: arranged rows (periods and rows) and columns (corresponding group) table based on increasing atomic mass.The discovery of the periodic law applies to the 1869 and undoubtedly belongs to the Russian scientist chemist - Dmitry Ivanovich Mendeleyev.While many foreign sources next to their name is mentioned the name of Yuliuas Lothar Meyer, who, according to them, a year later (but independently) has developed such a system.The key to the success of long-term efforts of the Russian chemist was the realization that previous attempts by other scientists failed, as many of the chemical elements have not yet been discovered, so he left his table for their vacancies.
Periodic Law, is displayed as a periodic table, horizontally divided into seven periods.The designations of first, second and third periods coincide with the same series of Roman numerals: I, II, III.Of the fourth, fifth and sixth divided into even and odd rows are identified by Roman numerals: IV, V, VI, VII, VIII and IX.A seventh period coincides with the X next.Vertical eighteen columns or columns all elements distributed across the eight groups.Each group of the first to seventh divided into two columns representing the primary and secondary subgroups.The eighth group consists of four sub-groups.Furthermore, two cells with chemical elements of the third group - lanthanum and actinium - hiding rows, respectively called lanthanides (58 to 71 number) and actinides (90 to 103 number).
In the first period, only two representative: hydrogen and helium.The second and third comprise eight chemical elements.Of the fourth, fifth and sixth are long, since each included eighteen visible elements, are distributed as follows: in the even rows contain ten and eight odd.But given the lanthanides, the sixth period, contains thirty-two chemical elements, including fourteen hidden.Seventh period is also long, he has eighteen, four of them visible, and fourteen (actinides) are hidden.The elements of odd rows of the fourth, fifth and sixth periods are sub-groups of (b), and the even rows are included in the main subgroups (a), along with those which belong to the first, second, third and seventh periods.
periodic law states that all of the elements within the same group differ considerable resemblance to each other and differ markedly from those that are part of other groups.For example, in group Ia, except hydrogen, include metals with chemical valence plus 1, while in group VIIa, except astatine, all elements are the nonmetals, which are compounds generally have a valence of minus 1. Today periodic law represented not onlytable.Mathematical expression, he has not, but there is a statement that the properties of any chemical element, and the properties of simple substances and complex compounds to which it is part, have a periodic dependence on the charge of the nucleus of an atom.
term periodicity was first proposed by Mendeleev, despite the fact that in the past there have been attempts of scientists from different countries somehow classifying certain chemicals.But it was he who noticed that when placing them in order of increasing atomic mass, the property of each element of the eighth resemble those of the first.In 1869, the first version of the table (at that time was known only 60 elements) is still very different from the modern look, visualize the periodic law.Over time, it has undergone some changes, which included the addition of new, later discovery of the chemical elements.But it's not only destroyed the idea of ​​periodicity of chemical properties of atoms, which guided the great Russian chemist, but each of them confirmed the law formulated by our scientists.
Open Russian scientist periodic law and create on its basis the periodic system have become a reliable foundation of modern chemistry.What makes Mendeleev corrected some of the atoms their mass and predicted the existence of three of nature yet undiscovered elements that later were experimentally confirmed, and were discovered gallium, scandium and germanium.All this has led to the universal recognition of the periodic system.The value of the periodic law can not be overemphasized, since this discovery was of great importance in the development of chemistry.
