Dmitri Mendeleev

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Dmitri Mendeleev bigraphy, stories - Chemists

Dmitri Mendeleev : biography

8 February 1834 – 2 February 1907

Dmitri Ivanovich MendeleevAlso romanized Mendeleyev or Mendeleef ( 8 February 1834 – 2 February 1907 O.S. 27 January 1834 – 20 January 1907) was a Russian chemist and inventor. He formulated the Periodic Law, created his own version of the periodic table of elements, and used it to correct the properties of some already discovered elements and also to predict the properties of elements yet to be discovered.

Periodic table

Mendeleev’s 1871 periodic table Sculpture in honor of Mendeleev and the periodic table, located in [[Bratislava, Slovakia]] In 1863 there were 56 known elements with a new element being discovered at a rate of approximately one per year.

Other scientists had previously identified periodicity of elements. John Newlands described a Law of Octaves, noting their periodicity according to relative atomic weight in 1864, publishing it in 1865. His proposal identified the potential for new elements such as germanium. The concept was criticized and his innovation was not recognized by the Society of Chemists until 1887. Another person to prose a periodic table was Lothar Meyer, who published a paper in 1864 describing 28 elements classified by their valence, but with no prediction of new elements. Meyer, who is often credited with the discovery of the periodic system, opposed and criticized the Periodic Law.

After becoming a teacher, Mendeleev wrote the definitive textbook of his time: Principles of Chemistry (two volumes, 1868–1870). As he attempted to classify the elements according to their chemical properties, he too noticed patterns that led him to postulate his periodic table. Mendeleev was unaware of the earlier work on periodic tables going on in the 1860s. He made the following table, and by adding additional elements following this pattern, developed his extended version of the periodic table., wou.edu, chemsheets.co.uk

Cl 35.5 K 39 Ca 40
Br 80 Rb 85 Sr 88
I 127 Cs 133 Ba 137

On 6 March 1869, Mendeleev made a formal presentation to the Russian Chemical Society, entitled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both atomic weight and valence. This presentation stated that

  1. The elements, if arranged according to their atomic weight, exhibit an apparent periodicity of properties.
  2. Elements which are similar regarding their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g., K, Rb, Cs).
  3. The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F.
  4. The elements which are the most widely diffused have small atomic weights.
  5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.
  6. We must expect the discovery of many yet unknown elements–for example, two elements, analogous to aluminium and silicon, whose atomic weights would be between 65 and 75.
  7. The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128. Here Mendeleev seems to be wrong as the "atomic mass" of tellurium (127.6) remains higher than that of iodine (126.9) as displayed on modern periodic tables, but this is due to the way atomic masses are calculated, based on a weighted average of all of an element’s common isotopes, not just the one-to-one proton/neutron-ratio version of the element to which Mendeleev was referring.
  8. Certain characteristic properties of elements can be foretold from their atomic weights.