Mendeleyev’s System of the Elements

4. The number of known elements kept on increasing during the 19th century. When chemists began to examine the characteristics of particular elements and compare them with each other, they realized that some elements showed considerable similarities in their chemical and physical characteristics. They began to sort similar elements into groups, organizing the elements within the groups according to their relative atomic weights. The various attempts to organize the elements into a system were crowned with success in 1869 and then published in a paper "A System of the Elements, arranged according to their Atomic Weights and Functions" by the Russian chemist Dmitri Ivanovich Mendeleyev (1834 – 1907). Independent of Mendeleyev's work, the German chemist, Lothar Meyer (1830 –1895), had arrived at similar conclusions. Whereas Mendeleyev's system first appeared in German chemistry journals in the spring of 1869, Meyer published his system in December of the same year.

5. Mendeleyev himself laid special emphasis on the periodicity of the elements, i.e. the recurrence of characteristics at discrete intervals on a scale where the elements were organized according to their increasing atomic weight. The elements were grouped into "periods". In Mendeleyev's System of 1869 these periods are represented by six vertical columns. In 1871, however, Mendeleyev introduced the horizontal representation of the periodic table, the system with the so-called "short periods". At present, the most usual representation of the table of the elements is in the form of long periods; the first period containing two elements, the second and third periods are eight elements each, the fourth and fifth periods eighteen elements each, the sixth period contains thirty-two elements. The seventh period is incomplete.

6. The System of the Elements, presented in 1869 and 1871, showed a number of gaps. Later on, it was improved. Mendeleyev's System of the Elements was recognized all over the world. Thanks to it many new elements have been discovered and are still being discovered by scientists.

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1. Where did Mendeleyev start ordering elements?

2. Why did Mendeleyev turn to ordering elements?

3. What did the researchers try to do to find some order of the elements?

4. What did scientists of Mendeleyev's time think about atoms of different elements?

5. How many columns are periods represented by?

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