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//@the_secrets_of_the_universe: The day the periodic table was born!Dmitri Mendeleev is famously known for developing one of the earliest periodic classifications of elements. On 17 February 1869, Mendeleev started classifying chemical elements known at the time by examining their atomic weights. He found that all chemical elements exhibited a recurring pattern or periodicity of properties within the group of elements. Based on this observation, he formulated a new law that said "elements arranged according to the value of their atomic weights present a clear periodicity of properties" and announced it before the Russian Chemical Society in March 1869. Mendeleev's first periodic table had 63 elements organized according to their atomic weights. Based on the relationship between chemical properties and atomic weights, Mendeleev predicted the existence of many other elements that were not yet discovered. These predictions included the existence of gallium, scandium, and germanium. He was so convinced by the law that he left gaps for them in the periodic table. All three elements were discovered within twenty years, with their properties matching his predictions exactly. For his achievements, Mendeleev received the Davy Medal from the Royal Society in London in 1882 and was honored with various awards and distinctions from other countries. Over time, more elements were found and added to the periodic table, and the modern periodic table now has 118 elements. It is widely utilized in chemistry, physics, and biology and remains a crucial tool for scientists, considered one of the most significant advancements in the history of science. #ThisDayInScienceHistory