This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
The periodic table now used to organize every element on the atlas descends from the work of the Russian chemist Dmitri Mendeleev, who published his first version in 1869 after noticing that arranging the known elements by atomic weight produced a table in which elements with similar chemical properties fell into recurring, regularly spaced columns. Mendeleev's boldest move was leaving deliberate gaps in his table for elements not yet discovered, and predicting the properties those missing elements would turn out to have.
Those predictions were tested within his own lifetime. Gallium, discovered in 1875, and germanium, discovered in 1886, both matched Mendeleev's predicted properties closely enough to convince most remaining skeptics that his arrangement reflected a genuine underlying order rather than a convenient bookkeeping scheme, and the periodic table has been revised and extended many times since without ever abandoning that same basic organizing logic.
Mendeleev's own path to the idea drew, by his own account, on years of trying to teach chemistry in a way students could actually retain, and the table's origin as a teaching tool is easy to forget once a version of it hangs on the wall of nearly every chemistry classroom in the world, treated today as simple settled fact rather than as the hard won result of one chemist's long search for an underlying pattern.