Question

Why does Cu have a greater atomic radius than that of Ni?

Answer 1

1. From Mn to Ni, atomic radii are almost constant because the increasing nuclear charge is balanced by electron-electron repulsions.
2. At Cu, the 3d shell is fully filled (3d¹⁰), increasing electron pairing.
3. More paired electrons cause greater electron-electron repulsions, which expand the electron cloud.
4. This expansion causes Cu to have a slightly larger atomic radius than Ni, despite the higher nuclear charge.

Hence, the atomic radius of Cu is greater than that of Ni due to increased electron-electron repulsions in the fully filled d-subshell, causing expansion of its electron cloud.