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Mendeleev

1834 - 1907 AD

Dmitry Mendeleev was a Russian chemist and he was the first periodic table of the elements. In this table, he divided the different elements according to their atomic weights. According to Mendeleev's system of arithmetic, the first periodic series contained seven elements for each series. The next seven periodicals contained seventeen items per series. The tables we use now depend mainly on Mendeleev's pioneering work.

When Mendeleev prepared his periodic tables for the first time, he realized that most of the
Elements not yet discovered, for example: the elements scandium and germanium, were not known in the time of Mendeleev.

But Mendeleev carefully studied the properties of the elements he knew, and from this study he knew where he could leave gaps in his schedule to accommodate the elements that would be discovered later. He also predicted the properties of these new elements. It was later found that these predictions are completely accurate when compared with the real properties of the elements.

Mendeleev also noticed that the chemical properties are repeated in different specific periods, and therefore he concluded that the chemical properties of the elements are periodic functions of their atomic weights.

In Mendeleev's table, the first two periodic or first two series had elements before any duplication of their properties occurred. In the third period, Mendeleev found that there were 17 elements before repeating their properties, and the fourth and fifth periods were also long chains.

Then the discovery of noble gases such as neon, argon, krypton, and xenon by Sir (William Ramsay), in addition to helium gas, which had been discovered before that, added an additional element to each periodic table in Mend Leif.