This scientist first organized the known elements by atomic weight and once organized, hypothesized that specific characteristics showed up periodically among the elements. The scientists is

The scientist who first organized the periodic elements according to its atomic weight was Alexander Emile Beguyer de Chancourtois. He was followed by John Newlands but they both had trouble arranging the properties because of some similarities that came out of the study.

It was Mendeleev who arranged the elements according to the atomic number that made the periodic table properly arranged he also knows that there are more elements that haven't been discovered.