Question

Higher values of ionisation energies of the 5d-transition elements are consistent with the:

• A. relative smaller effective nuclear charge
• B. relatively smaller size of their atoms
• C. relatively smaller penetration
• D. all the above are correct

Answer 1

The correct option is B relatively smaller size of their atoms

In the $5d$-series of transitions elements, after lanthanum $\left(La\right)$, the added electrons go to the next inner $4f$ orbitals. The $4f$ electrons have poor shielding effect. As a result, the outermost electrons experience greater nuclear attraction. This leads to higher ionisation energies for the $5d$- series of transition elements.