Question

Without knowing the electronic configurations of the atoms of elements, Mendeleev still could arrange the elements nearly close to the arrangements in the Modern Periodic Table. How can you appreciate this?

Answer 1

Mendeleev arranged the elements on the basis of atomic masses. He arranged the elements with same properties in same group. So, without knowing electronic configuration of atoms of elements, he still could arrange the elements similar to Modern Periodic Table, where periodicity was observed in the properties of the elements he arranged.