The periodic table of chemical elements is ordered according to the chemical and physical characteristics. Dimitri Mendeleev ordered the elements on the basis of their chemical properties. Julius Lothar Meyer ordered them according to the physical properties of their atoms. The evolution of the periodic table is relationed with the discovery of the elements, the study and classification of their common properties, the atomic mass or "atomic weight" and more recently the atomic number and the relationships between the atomic mass and periodic properties of the elements. In the early decades of the 20th century began to developed the Quantum theory. The application of this theory results in a new sort of the elements depending on the electronic structure of their atoms and the prediction of their different chemical properties.