Сборник текстов на казахском, русском, английском языках для формирования навыков по видам речевой деятельности обучающихся уровней среднего образования

The early innovation of Periodic law by a Russian chemist, Dmitry I. Mendeleev in the mid-19th century, has been of great value in the growth of chemistry. In chemistry, Periodic law is the arrangement of theelements in order of increasing atomic number, that is, the total number of protons in the atomic nucleus and their physical and chemical properties recur in a pattern with the increasing atomic number. In the periodic table, the horizontal rows, known as the “periods” exemplify these relations. In fact, until the second decade of the 20th century, it was not documented that the order ofelements in the periodic system is that of their atomic numbers.

Classification became necessary due to the increase in the number of elements discovered. In 1817, J.W. Dobereiner, a German chemist , explained that the atomic weight of strontium rests in the middle between that of calcium and barium, and few years later he demonstrated that other such “triads” such as chlorine, bromine, and iodine and lithium, sodium, and potassium are also present. Other scientists, during1827 and 1858 developed analogous relationships which extended more than the triads of elements, fluorine being added to the halogens and magnesium to the alkaline-earth metals, while oxygen, sulfur, selenium, and tellurium were classed as one family and nitrogen, phosphorus, arsenic, antimony, and bismuth as one more element family. De Chancourtois, a French scientist, in 1862 anticipated a classification of the elements based on the new values of atomic weights. It was finally the Russian chemist, Mendeleev, who proposed the periodic law, which indicated that the elements arranged in the increasing order of atomic weights show a periodic change of properties. In 1869, the first periodictable was tabulated by Mendeleev. It had 17 columns, with two nearly complete periods of elements, frompotassium to bromine and rubidium to iodine, lead by two fractional periods of seven elements each (lithium to fluorine and sodium to chlorine), and three incomplete periods.

• 
  Innovation of New Elements: Through Mendeleyev’s efforts in 1871, the grand significance of the periodic law was made apparent in predicting that the properties of the 17 elements could be interrelated with those of other elements by relocating the 17 to new positions from those shown by their atomic weights. The subsistence of many of the properties of uninvented elements of that time like eka-boron, eka-aluminum, and eka-silicon, now identified with the elements scandium, gallium, and germanium, was also predicted by Mendeleev. Likewise, following the discovery of helium and argon, the periodic law allowed the discovery of the subsistence of neon, krypton, xenon, and radon. Besides, the absence of element 72 was anticipated, from its position in the periodic system, to be alike to zirconium in its properties rather than to the rare earths, was shown by Niels Bohr, a Danish physicist. In 1922, other scientists also examined zirconium ores following Bohr’s prediction.
  
• 
  Implication of atomic numbers: A number of of the elements in the
  

Starting in 1913, thorough knowledge of the the elements and their properties had improved. Followed by the exclusion principle by the Austrian theoretical physicist, Wolfgang Pauli in 1925, the invention of the spin of the electron by George E. Uhlenbeck and Samuel Goudsmit in 1925, and the development of quantum mechanics by Werner Heisenberg were the significant advanced inventions which developed the periodic law. The development of the electronic theory of valence and molecular structure, beginning with the postulate of the shared electron pair by the chemist, Gilbert N. Lewis in 1916, also played a vital role in elucidating the periodic law. [6]

"If all the elements are arranged in the order of their atomic weights, a periodic repetition of properties is obtained. This is expressed by the law of periodicity." Dmitri Mendeleev, Principles of Chemistry, Vol. 2, 1902, P. F. Collier, p17.

1. 
   A higher atomic weight than the one on its left. For example, magnesium (atomic weight 24.3) is placed to the right of sodium (atomic weight 23.0):
   

2. 
   Similar chemical properties to other elements in the same column - in other words similar chemical reactions. Magnesium, for example, is placed in the alkali earths' column:
   

progress. With the benefit of hindsight, we know that Mendeleev's periodic table was underpinned by false reasoning. Mendeleev believed, incorrectly, that chemical properties were determined by atomic weight. Of course, this was perfectly reasonable when we consider scientific knowledge in 1869.