Periodic table's size and shape have changed since 1923

Nearly one-fourth (23%) of all the known elements (those in color) have been added to the periodic table since 1923, including all 20 that have atomic numbers greater than that of uranium, element 92. Most of the new elements (those in red) were first created synthetically through nuclear reactions, although several of these elements were later found to be naturally occurring as well. A new row, representing the actinide series, was added to the periodic table in 1945. Elements in color with atomic numbers smaller than that of uranium were assumed to exist but were undiscovered in 1923; those in blue were discovered by isolation from natural sources.