Mandleev arranged the elements on the basis of increasing order of the atomic masses of the elements.
He divided the 63 elements which were known or discovered at that time.
There were 8 groups and 6 periods in his Periodic Table.
Most importantly he made cards of every element , and wrote the reactions of that element with hydrogen and oxygen. Thus he found the similarities in the chemical formulae also, and he found taht these were related to the mass of elements.