Home Chemistry Classification of Elements and Periodicity Mix Poor shielding of nuclear charge by d or f- …
Chemistry Classification of Elements and Periodicity Mix Single Correct MCQ
Published on: August 13, 2026

Poor shielding of nuclear charge by d or f- orbital electrons is responsible for which of the following facts ?

A
Atomic radius of Nb (4d-series) is comparable to that of Ta (5d-series)
B
The Istionisation enthalpy of copper is less than that of zinc
C
The value of electron gain enthalpy is more negative for sulphur than for oxygen.
D
The Istionisation energy for gold is greater than that of silver.

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(a, d)

The d and f orbitals do not shield the nuclear charge very effectively .Therefore there is significant reduction in the size of the ions, just after d or f orbitals have been filled completely. This is called lanthanide contraction. Atomic radii of Nb (Nb3+ = 0.72 Å) and Ta (Ta3+ = 0.72 Å) are almost identical due to lanthanide contraction.

This is also the reason for the higher ionisation energy of gold than silver.

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