Why did Dmitri mendeleev reverse the order of some elements in the periodic table?

Answer 1

He was bold enough to reverse the order of some pairs of elements and to predict that their atomic masses were incorrect. Some of these predictions were correct, but others were not, because we now know that the fundamental basis of the periodic table is atomic number rather than Atomic Mass.

Answer 2

Dmitri Mendeleev first arranged the Periodic Table by the mass of the atom. He later realized that the elements should be arranged by the number of protons in each nucleus, so he had to reverse the order of some of the elements.

Answer 3

Mendeleev did that in order to group the element with similar characteristics. In modern periodic table , elements are arranged in order of atomic masses and no need of reversing the elements was foud.