While writing his textbook Principles of Chemistry, Dmitri Mendeleev created a card containing the symbol, atomic mass, and the chemical and physical properties for each of the
63 known elements. Mendeleev laid the cards out in various organizational patterns until he grouped elements with similar properties in vertical columns. Mendeleev developed his statement
of the periodic law based on the patterns observed in his table.
Although Mendeleev’s periodic table is over 130 years old, it resembles the periodic tables that are in the today’s chemistry classroom. Modern periodic tables arrange the elements
by increasing atomic number thanks to H.G. Moseley’s work around 1913. Glenn T. Seaborg made the last major change to the periodic table when he added the lanthanide series and actinide
series in the 1945 to accommodate the newly discovered transuranium elements.