when did he invent the system mentioned above?
1869
Dmitri Mendeleev
 On 6 March 1869, he made a formal presentation to the Russian Chemical Society, titled "The Dependence between the Properties of the Atomic Weights of the Elements", which described elements according to both atomic weight (now called "relative atomic mass") and valence. This presentation stated that
what is hassium? It is a chemical element. where is it naturally found? It is not known to occur naturally on Earth. is it used in any fusion reactions? Yes, it was used in Cold fusion. where does the name of the element come from? Under Mendeleev's nomenclature, It would be known as "eka-osmium", as in "the first element below osmium in the periodic table". what are the physical properties of the above-mentioned element? It should crystallize in the hexagonal close-packed structure. where is this used? It is used in the field of Experimental chemistry. are any precautions needed while using it? UNANSWERABLE what is the table used to describe the elements? periodic table who invented this system? Dmitri Ivanovich Mendeleev where was he born? In the village of Verkhnie Aremzyani, near Tobolsk in Siberia.
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Dmitri Mendeleev [SEP] Periodic table
After becoming a teacher in 1867, Mendeleev wrote the definitive textbook of his time: "Principles of Chemistry" (two volumes, 1868–1870). It was written as he was preparing a textbook for his course. This is when he made his most important discovery. As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his periodic table; he claimed to have envisioned the complete arrangement of the elements in a dream: Unaware of the earlier work on periodic tables going on in the 1860s, he made the following table: By adding additional elements following this pattern, Mendeleev developed his extended version of the periodic table.