In those days, chemists hadn’t yet fully grasped the nature of atoms, as described in the atomic theory proposed by English schoolteacher John Dalton in 1808. In fact, German chemist Johann Wolfgang Döbereiner noticed peculiarities in groupings of elements as early as 1817.
Mendeleev had been thinking about grouping the elements for years, and other chemists had considered the notion of relationships among the elements several times in the preceding decades. Legend has it that Mendeleev conceived and created his table in a single day: February 17, 1869, on the Russian calendar (March 1 in most of the rest of the world). Historic Images/Alamy Stock Photo Laying the groundwork The periodic table symbolizes not merely the constituents of matter, but the logical cogency and principled rationality of all science. His table finished the transformation of chemical science from the medieval magical mysticism of alchemy to the realm of modern scientific rigor. It hinted at the existence of subatomic structure and anticipated the mathematical apparatus underlying the rules governing matter that eventually revealed itself in quantum theory. It validated the then-controversial belief in the reality of atoms. Mendeleev’s table did more than foretell the existence of new elements.
“The law of periodicity first enabled us to perceive undiscovered elements at a distance which formerly was inaccessible to chemical vision.” “Before the promulgation of this law the chemical elements were mere fragmentary, incidental facts in Nature,” Mendeleev declared. His law revealed profound familial relationships among the known chemical elements - they exhibited similar properties at regular intervals (or periods) when arranged in order of their atomic weights - and enabled Mendeleev to predict the existence of elements that had not yet been discovered. Mendeleev’s table looked like an ad hoc chart, but he intended the table to express a deep scientific truth he had uncovered: the periodic law. “The periodic table,” wrote the chemist Peter Atkins, “is arguably the most important concept in chemistry.”
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