The periodic table is the most powerful tool chemists have for organizing chemical information. Without it, chemistry would be a chaotic, confusing jumble of seemingly random observations. What makes the periodic table really invaluable is its use as a predictive tool. You can predict a lot about the chemical behavior of an element if you know where it is on the periodic table. We give credit to Dmitri Mendeleev for the first Periodic Table. He organized the elements in his table in order of atomic mass. Henry Moseley modified the table, ordering the elements in terms of atomic number. This is the periodic table we use today.