The periodic table of elements was proposed in 1869, and thereafter became one of the cornerstones of the natural sciences. This table was designed to contain all the elements found in nature in a special layout that groups them in rows and columns according to one of their most important characteristics, the number of electrons. Scientists have used the periodic table for decades to predict the characteristics of the then-unknown elements, which were added to the table over time.
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Source: Phys.org