The Periodic Table
In the mid 19th centuries, as more and more elements were getting discovered in chemistry, the problem of classifying meaningfully them became apparent. One person who took up this problem as a challenge was a Russian chemist, Dmitri Mendeleev. But it was not an easy problem to solve. Till that time only sixty odd out of the ninety three elements were known. Mendeleev's attempts to conceptualise them by atomic weights failed because of the gaps in the knowledge.
Then one night in 1869, weary after his frustrating attempts to find the answer, he went to sleep. He reported:
"I saw in a dream a table where all the elements fell into places as required. Awakening I immediately wrote it down on a piece of paper. Only in one place did a correction later seemed necessary".
This is how the Periodic Table of Elements was discovered. So accurate was this table, that Mendeleev could predict the properties of elements, which were not even discovered till then.
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