Question

What is the correct order of covalent size of the following ?

Cu ___ Ni

• A. Cu = Ni
• B. Cu < Ni
• C. Cu > Ni
• D. None of these

Answer 1

The correct option is C Cu > Ni

The covalent size of the Cu is greater than the Ni because Cu has $3d^9$ configuration while Ni has $3d^8$ configuration.
Hence, more the d electrons more will be screening effect , leading to lesser nuclear attraction, for the outer $4s$ orbital electrons. Hence, the size is lesser contracted.
So, the effective nuclear charge of Ni will be more, due to lesser d electrons and hence, lesser screening effect , leading to more effective nuclear charge, making smaller covalent radius than Cu.