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

Answer

Mendeleev used atomic weight as the basis of classification of elements in the periodic table. He arranged the then know elements in order of increasing atomic weights grouping togther elements with similar properties. Mendeleev relied on the similarities in the properties of the compound formed by the elements. He realized that some of the elements did not fit in with his scheme of classification if the order of atomic weight was stricktly followed. He ignored the order of atomic weights and placed the elements with similar properties togther. For example, iodine with lower atomic weight than telliumn group `16` was placed in group `17` along with fluroine, chlorine, etc. because of similartities in properties. Thus Mendellev did not stick strictly to arrangement of elements in the increasing order of atomic weight.