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 in the periodic table. He arranged the then known elements in order of increasing atomic weights grouping together elements with similar properties. He stuck to this basis leaving out blank spaces where elements were not known at that time. For example, the element gallium after aluminium and germanium after silicon were not known at the time Mendeleev prepared his periodic table. He called these elements as eka-aluminium and eka-silicon. Later, these elements were discovered and their properties were found to be similar to those predicted by Mendeleev.