Question

Why is there an increase in the atomic radius of transition elements at the end of the period?

• A. Increased electron-electron repulsions
• B. Decreased electron-electron repulsions
• C. Increase in nuclear charge
• D. Increase in atomic mass

Answer 1

The correct option is A Increased electron-electron repulsions

Across the period in transition elements, the nuclear charge increase due to poor shielding of d-orbitals which results in attraction of valence electrons and the size decrease.
Also, the number of electrons in (n-1) d orbitals increase as we go from left to right which increase the repulsion between the electrons.

Near the end of the transition series, the increased electron-electron repulsions between added electrons in the same orbitals dominates the attractive forces due to increased nuclear charge. This results in the expansion of the electron cloud and therefore, increases the atomic size.