He produced the 'law of octaves'. He assumed all elements had been found, so filled all octaves even though some weren't similar so other scientists rejected it. Also ordered them in atomic weight
What did Mendeleev do?
Mendeleev ordered elements in atomic weight. He left gaps for undiscovered elements, he used these gaps to predict the properties of the undiscovered elements
What did Moseley do?
He ordered them in atomic number, how they are arranged today
