Mendeleev arranged the elements in rows in order of increasing mass so that elements with similar properties were in the same column.
The discovery of new elements such as gallium demonstrated the usefulness of Mendeleev’s table because the close match between Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be.
Mendeleev’s efforts more successful because he provided an organizing principle that worked for all off the known elements.
