Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?

Explanation

Mendeleev used atomic weight as the basis of classification of elements and arranged elements in the order of increasing atomic weights. He sincerely stuck to this basis and left blank spaces for the elements which were not known that time. On the basis of their atomic weights, he also predicted their properties. His predictions were remarkably found correct later on, when these elements were discovered.