His renowned work Osnovy khimii The Principles of Chemistry, —71 was published in two volumes. The Principles of Chemistry became the definitive textbook on the subject at the time , ran through many editions and was widely translated. Mendeleev later rated it as one of his four major contributions to science ; the others being the periodic table, the elasticity of gases, and understanding of solutions as associations. Though several earlier attempts had been made to classify the chemical elements, the first person to arrange the elements in order of their relative atomic masses then called atomic weights and notice their periodicity was French geologist A.
However, as he used geological terms and as his chart included ions and compounds, his publication was ignored by chemists. Many other chemists made significant progress in the formulation of a periodic table, most notably John Newlands. However, it was Dmitri Mendeleyev who first published a periodic table similar to the modern one we use today, in German chemist Julius Lothar Meyer independently arrived at a periodic table similar to Mendeleev but he published it a year later.
In his presentation, which was entitled The Dependence between the Properties of the Atomic Weights of the Elements , he described chemical elements according to both atomic weight and valenc y. He stated several important points during the presentation including the Periodic law , which states that when elements are ordered according to their atomic weight s , certain properties of elements repeat periodically.
Though other scientists, like Newlands, also noted periodicity of elements, the credit of the discovery is given to Mendeleev and Meyer. Mendeleev arrived at the law independently from investigations of other scientists. Unlike other chemists, Mendeleev put the elements of the periodic table in their correct places. At the time, atomic weights were determined by multiplying equivalent weight with valency. Sometimes these were incorrect due to wrong valency assigned to an element. Like beryllium was given a valency of 3 due to which its atomic weight came out to be However Mendeleev said that the valency was 2 to fit it into the space between Li and B.
Similarly, Mendeleev proposed that atomic weights of some elements had been measured incorrectly and his predictions soon turned out to be true! The most spectacular accomplishments of Mendeleev was that he not only left gaps in his periodic table f or elements which were not yet discovered but more importantly predicted the properties of some of these elements and their compounds. Three of these elements were discovered within 15 years while Mendeleev was alive.
Though many other scientists made important contributions in the development of the Periodic Table, Dmitri Mendeleev was the first chemist to use the trends in his periodic table to correctly predict the properties of missing elements, such as gallium and germanium; and to ignore the order suggested by the atomic weights of the time, to better classify the elements into chemical families.
Also, as his predictions started to come true, more and more people took notice of his work helping in establishing the importance of the Periodic Table. He considered solutions as liquid systems in a state of dissociation. According to him, these systems consist of molecules of the solvent and solute and of products of their interaction.
His views on the nature of solutions and vast experimental data concerning the same were presented in his monograph Study of Aqueous Solutions From Their Specific Gravity. So convinced was he of the soundness of his periodic law that he left gaps for these elements in his table. Within twenty years, all three had been found, and their properties confirmed his predictions almost exactly. Mendeleev himself was surprised by how fast his ideas were confirmed.
As news of his remarkable accomplishment began to spread, Mendeleev became something of a hero, and interest in the periodic table soared. In all, Mendeleev predicted 10 new elements, of which all but two turned out to exist. He later proposed that the positions of some pairs of adjacent elements be reversed to make their properties fit into the periodic pattern.
He suggested swapping cobalt with nickel and argon with potassium, which he believed had been wrongly placed because their true atomic weights were different from the values chemists had determined.
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