After the conference Stanislao Cannizzaro, acknowledging the work of fellow Italian Amedeo Avogadro on chemical formulae and valency, produced the most accurate list of atomic weights then known. This work would later prove to be essential to Mendeleev in recognising periodicity.
Mendeleev returned to St Petersburg University, initially as a professor of chemistry in the technological section. Pressurised by his sister, he married Feosva Leshchevayi, six years his senior, and together they had a son Vladimir and daughter Olga. But Mendeleev was a workaholic, his science always came before his marriage, and his wife lived mainly alone with the children at an estate near Moscow, some miles away.
In Mendeleev was appointed to the chair of inorganic chemistry at the university, and finding no suitable textbook for his students he wrote his own - Osnovy khimii Principles of chemistry , which ran to eight editions, some of which have been translated into English, German and French. Today these rooms are filled with furniture, mostly from the family, chemical apparatus, paintings and books, some bound by Dmitri himself.
Fairly remote in Russia Mendeleev was unaware of other chemists' attempts, including de Chantcourtois, Newlands, Odling, Hinrichs, and Lothar Meyer, to organise the elements discovered so far. Meanwhile he continued to collect information about each element and wrote this down on separate cards. On 17 February 1 March in our Gregorian calendar while arranging the cards in a way similar to playing a game of patience, he suddenly saw an emerging pattern of repeated properties when elements were listed in increasing weight order.
This he initially called the Periodic System but in an improved version in he referred to it as a Periodic Table. In Russia today it is often referred to as the Mendeleev Table.
The first public announcement of the Periodic System came a month later to the recently formed Russian physicochemical society by Professor Menschutkin because Mendeleev was ill. Mendeleev's Table was superior to earlier tables in two important ways. First he amended the atomic weights of some elements to place them correctly in the Table with properties related to adjacent elements, particularly in the same column.
Secondly, he left spaces for yet to be discovered elements whose properties he boldly predicted. Nevertheless, Mendeleev's Periodic System, an idea from a distant land, was not initially accepted by other chemists. There were two reasons for some atomic weights to be amended - either they had been assigned the wrong valency or they had unusual isotopic abundances. In the case of beryllium, for example, its combining weight was 4. Chemically it resembled aluminium, having a white amphoteric hydroxide, and so it was assigned a valency of three, and thus an atomic weight of Mendeleev pointed out that there was no space for an element between carbon and nitrogen, but with valency of two it would fit above magnesium.
Thus beryllium was correctly placed by an atomic weight change. Similar situations occurred with uranium and indium. We now know that elements are ordered in increasing atomic number and not atomic weight, but fortunately for Mendeleev and other contemporary chemists there are only three cases Ar-K, Co-Ni and Te-I among stable elements where the two orders differ.
In argon was unknown, and Co and Ni had chemical properties and atomic weights so similar that it was not a problem that Ni preceded Co. The difficult case to explain was Te-I. The accepted atomic weight of tellurium was more than that of iodine , yet chemically iodine more closely resembled bromine. Mendeleev was convinced of the accuracy of his Table, so he reasoned that one of the atomic weights had to be wrong, probably the less familiar tellurium.
His experimental assistant, Bohuslav Brauner, determined the molecular weight of a volatile halide to obtain a lower atomic weight of tellurium. He was so convinced of the expected result that when the atomic weight of tellurium was still too high he concluded that he must have failed to remove some heavy impurity.
So tellurium was correctly placed in the Table but the amendments to its atomic weight were wrong. We now know that the anomaly arises because of the great abundances of the two heaviest tellurium isotopes, unlike iodine which unusually is monoisotopic.
Twenty five years later the discovery of argon posed a similar problem. When he did this he noted that the chemical properties of the elements and their compounds showed a periodic trend.
He then arranged the elements by putting those with similar properties below each other into groups. To make his classification work Mendeleev made a few changes to his order:. Mendeleev left gaps in his table to place elements not known at the time. In , just five years after John Newlands put forward his Law of Octaves, a Russian chemist called Dmitri Mendeleev published a periodic table.
Mendeleev also arranged the elements known at the time in order of relative atomic mass , but he did some other things that made his table much more successful. He realised that the physical and chemical properties of elements were related to their atomic mass in a repeating or 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.
His father, Ivan Pavlovich Mendeleyev, went blind around the time his final son was born, and died in The scientist's mother, Mariya Dmitriyevna Kornileva, worked as the manager of a glass factory to support herself and her children.
When the factory burned down in , the family moved to St. Mendeleyev attended the Main Pedagogical Institute in St. Petersburg and graduated in After teaching in the Russian cities of Simferopol and Odessa, he returned to St. Petersburg to earn a master's degree. Mendeleyev continued his studies abroad, with two years at the University of Heidelberg. As a professor, Mendeleyev taught first at the St. Petersburg Technological Institute and then at the University of St.
Petersburg, where he remained through Realizing he was in need of a quality textbook to cover the subject of inorganic chemistry, he put together one of his own, The Principles of Chemistry.
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