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.

Question

In Mendeleev&rsquo;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.

Philoid · Accepted Answer

Because the properties of cobalt were similar to those of rhodium (Rh) and iridium (Ir) (same group) and the properties of nickel were similar to those of palladium (Pd) and platinum (Pt) (same group). So cobalt with atomic mass of 58.93 amu was placed before nickel having an atomic mass of 58.71 amu.