Mendeleev's Periodic Table

In 1868, Dmitri Mendeleev was a professor of chemistry at St. Petersburg University, tasked with writing a textbook. He faced a fundamental problem: how to organize the 63 elements known to science? They were a confusing mix of metals like iron and gases like oxygen, often grouped by simple traits, but with no unifying logic. Previous attempts to find a system, like the ‘Law of Octaves,’ had been dismissed or were incomplete. For Mendeleev, teaching chemistry without a clear structure was impossible. He needed to find a hidden pattern, a law that could bring order to the elemental chaos. His search began not in a lab, but with the pages of his unfinished book.