what pattern did mendeleev discover
Protons & Atomic Number. 1  In 1869, the Russian scientist Dmitri Mendeleev discovered a set of patterns in the properties of the elements. 2  He noticed that a pattern of properties appeared when he arranged the elements in order of increasing atomic mass. In the periodic table, the properties of the elements repeat in each period, or row, of the table. 2  Mendeleev left three blank spaces in the table. 3  He predicted that these spaces would be filled by elements that had not yet been discovered.