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We can clearly see the Periodic Table everywhere. It is one of the most important and successful chemistry discoveries to date. To make the completed and latest periodic table, there are a lot of scientists and chemists who have been involved. One of the chemists who have involved most is Dmitri Mendeleev who was from Russia. He has supported a lot finding the elements and the first who used Periodic Law in his Periodic Table.
What has Mendeleev included in periodic table? Does Mendeleev ‘s periodic table have any mistakes?
Although Mendeleev‘s table has brought a lot of support to develop the latest table, there are several reasons which shows that there were still some mistakes in his table that has been found.
By the time Mendeleev becoming a teacher in 1867, he has written a textbook which called Principles of Chemistry (1868-1870). The first reason why he wrote the book was to prepare for his course. This was when he made his most important and popular discovery. When he tried to classify the elements in accordance to their chemical properties, he observed patterns that led him to postulate his periodic table; he claimed to have anticipated the complete association of the elements in a dream. He said that:“I saw in a dream a table where all elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper, only in one place did a correction later seem necessary“. Mendeleev’s dream of the periodic table of elements in its completed form is apparently specious, despite repeated citations. Not only is there no dream report but evidence rests on a colleague’s second-hand account. Kedrov’s examination of archival material indicates that Mendeleev had already discovered the periodic table before the alleged dream took place; and that a dream quite plausibly occurred somewhat later that depicted an improved representation of the periodic table. Mendeleev had developed the completed version of the periodic table and he had made a formal presentation to the Russian Chemical Society, titled “The Dependence between the Properties of the Atomic weights of the Elements”. There are several differences between Mendeleev’s periodic table and the latest periodic table. Firstly, Mendeleev‘s periodic table based on the atomic mass but our table based on the atomic number. Next, it is the number of elements. When our table has about 118 elements, Mendeleev table contains about 66 elements. In Mendeleev’s periodic table transition elements included with other elements. In Modern periodic table transition elements placed in separate block. According to Mendeleev’s, the isotopes with different atomic weights, should be placed in different positions, but are not given any position and no justified reason was explained. In Modern periodic table, the isotopes were assigned same position as they have same atomic number.
The primary idea of the system is that the factors be arranged in the order of their atomic masses. The chemical properties return periodically so that elements with same properties divide in one group with the Periodic law’s arrangement. The only one mistake here is iodine, which is certainly the chemical analog of bromine not selenium, had a smaller atomic mass than tellurium, whose resemblance to selenium was beyond any doubt. Tellurium was already found before iodine by Julius Lothar Meyer in his system of elements in 1864. Mendeleev did not agreed with the experimentally determined atomic mass for tellurium, but assumed a exceptionally small error. However, this did not remedy the problem for a long time; the mistake of the anomalous atomic mass of tellurium kept returning in his later years as well. His most creative answer used to be that tellurium has a larger than expected atomic mass because it was once now not only organized in an entirely pure form however contained some of its heavier analog dvi-tellurium.
It is even more instructive to think about the instances where modern discoveries did not have same point with Mendeleev’s predictions. Firstly, the 63 elements in the primordial periodic table do now not consist of both terbium and erbium today is credited to Henri Moissan. It can be explained by way of the fact that fluorine was once identified to be an element and named long before it was isolated. The elements erbium and lanthanum are quoted with atomic masses that are nowhere near the latest values. Finally, there is a symbol Di in row 8. (Lente, 2019).
However, these mistakes and contradictions are almost natural consequences because of small and limited knowledge of chemistry at that time. The history of science lists many more mistakes than the actual number of chemical elements. We should also agree that Mendeleev changed the atomic masses of some other elements as well and turned out to be correct. For example, beryllium used to be frequently assigned an atomic mass of 14 at that time, which is the same as that of nitrogen. Based on property similarity, Mendeleev proposed that the valence of beryllium was once assigned and that its real atomic mass must be the non-integer fee of 9.4, which placed it right above magnesium.
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