Dmitri Mendeleev (TABLE; He described elements according to both atomic weight (now called relative atomic mass) and valence.) (jan 1, 1869 – may 18, 1869)
Description:
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.Added to timeline:
Date:
jan 1, 1869
may 18, 1869
~ 4 months and 17 days