In Mendeleev’s Periodic Table,


In Mendeleev’s Periodic Table, the elements were arranged in the increasing order of their atomic masses. However, cobalt with atomic mass of 58.93

amu was placed before nickel having an atomic mass of 58.71 amu. Give reason for the same.


This is regarded as a defect in the Mendeleev’s periodic table. However, the main reason for making the arrangement was that the elements with

similar characteristics must be grouped together. In this case,

• Cobalt (Co) should be in the company of the elements Rhodium (Rh) and Iridium (Ir).

• Nickel (Ni) should be in the company of the elements Palladium (Pd) and Platinum (Pt).

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