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In 1889, Mendeleev created the "law of periodicity" The Law of periodicity is the concept in which each element increases as the mass of the atom increases. During his lifetime there was only sixty three found elements he knew that there were elements still not found so he left space in the periodic table including space for the noble gases in which have not been discovered. "http://reich-chemistry.wikispaces.com/Dmitri-Mendeleev"