Question

In mendeleev periodic table the elements were arranged in the increasibg order of their atomic masses's. however, cobalt with atomic mass of 58.93amu was placed before nickel having atomic mass 58.71amu. give reasons for the same.

Answer 1

There are Some pairs of elements, like cobalt and nickel, in which element with higher atomi Mass was placed before the lower atomic mass element. It was done in order to maintain the similarity in chemical properties of elements belonging to same group.

Answer 2

due to the elements chemical property it had been placed in that way. as he formulated his periodical table in a way that have similar chemical and physical properties