We can clearly see the periodic table everywhere. It is one of the most important and successful chemical discoveries to date. To make the complete and latest periodic table, many scientists and chemists were involved. One of the chemists who has been most involved is Dmitri Mendeleev, originally from Russia. He greatly supported the search for the elements and was the first to use the Periodic Law in his Periodic Table. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essayWhat did Mendeleev include in the periodic table? Does Mendeleev's periodic table contain any errors? Although Mendeleev's table provided a lot of support to develop the last table, there are several reasons that show that there were still some errors in his table that was found. When Mendeleev became a teacher in 1867, he wrote a textbook entitled Principles of Chemistry (1868-1870). The first reason he wrote the book was to prepare for the course. It was then that he made his most important and popular discovery. When he tried to classify elements based on 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 in which all the elements arranged themselves as required. When I woke up I immediately wrote it down on a piece of paper, only in one point did I feel it needed a correction." Mendeleev's dream of the periodic table of elements in its complete form is apparently specious, despite repeated citations. Not only is there no dream report, but the evidence is based 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 occurred; and that, most likely, some time later a dream occurred describing an improved representation of the periodic table. Mendeleev had developed the complete version of the periodic table and made a formal presentation on it to the Russian Chemical Society, entitled “The Dependence between the Properties of the Atomic Weights of the Elements.” There are many differences between Mendeleev's periodic table and the more recent periodic table. First Mendeleev's periodic table based on atomic mass, but our table based on atomic number. Next, is the number of elements. When our table has about 118 elements, the Mendeleev table contains about 66 elements. In Mendeleev's periodic table transition elements are included with other elements. In the modern periodic table the transition elements are placed in separate blocks. According to Mendeleev, isotopes with different atomic weights should be placed in different positions, but no position is given and no justified reason has been explained. In the modern periodic table, isotopes are assigned the same position because they have the same atomic number. The main idea of ​​the system is that the factors are arranged in the order of their atomic masses. Chemical properties return periodically so that elements with the same properties divide into a group according to the arrangement of the periodic law. The only mistake here is that iodine, which is certainly the chemical analogue of bromine and not selenium, had an atomic mass lower than that of tellurium, whose similarity to selenium was beyond doubt. Tellurium had already been found before iodine by Julius Lothar Meyer in his system of elements in 1864. Mendeleev disagreed with the experimentally determined atomic mass for tellurium, but hypothesized.