The periodic table of the elements is a systematic way of listing and cataloging all of the naturally occurring and man-made chemical elements that make up all of the matter in the known universe. What became the modern periodic table was independently first published in 1869 by Russian chemist Dimitri Mendeleev and in 1870 by German chemist Julius Lothar Meyer. They first developed a table with recognizable groups and periods (horizontal and vertical groups) that organized elements by their properties into similar groups. Mendeleev's table was the one to become universally accepted for two major reasons. First, he left strategic gaps in his table to account for elements that had not yet been discovered (and subsequently were discovered and fit the expectations required in his periodic table). Also, Mendeleev switched the order of a few elements around in his table despite their apparent molecular weights because their properties made more sense that way. More refined measurements of atomic properties in later years showed that Mendeleev was actually correct in his listing versus Meyer's table.