Periodic Table of the Elements

'Father' of the periodic table
Dmitri Mendeleev, a Russian chemist and inventor, is considered the "father" of the periodic table, according to the Royal Society of Chemistry. In the 1860s, Mendeleev was a popular lecturer at a university in St. Petersburg, Russia. Since there were no modern organic chemistry textbooks in Russian at that time, Mendeleev decided to write one, and simultaneously tackle the problem of the disordered elements. 

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Putting the elements in any kind of order would prove quite difficult. At this time, less than half of the elements were known, and some of these had been given wrong data. It was like working on a really difficult jigsaw puzzle with only half of the pieces and with some of the pieces misshapen.

Mendeleev ultimately wrote the definitive chemistry textbook of his time, titled "Principles of Chemistry" (two volumes, 1868–1870), according to Khan Academy. As he was working on it, he came upon a significant discovery that would contribute greatly to the development of the current periodic table. After writing the properties of the elements on cards, he began ordering them by increasing atomic weight, according to the Royal Society of Chemistry. This is when he noticed certain types of elements regularly appearing. After intensely working on this "puzzle" for three days, Mendeleev said that he had a dream in which all of the elements fell into place as required. When he woke up, he immediately wrote them down on a piece of paper — only in one place did a correction seem necessary, he later said.

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Mendeleev arranged the elements according to both atomic weight and valence. Not only did he leave space for elements not yet discovered, but he predicted the properties of five of these elements and their compounds. In 1869, he presented the findings to the Russian Chemical Society. His new periodic system was published in the German chemistry periodical Zeitschrift fϋr Chemie (Journal of Chemistry).