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

Question

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

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 `1^(st)` ionisation 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 `1^(st)` ionisation energy for gold is greater than that of silver.

Monjur Alahi

5 views

2025-01-04 04:42

1 Answers

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Salim Ahmed Kawsar · Accepted Answer · 2023-02-05T15:29:48+06:00

Correct Answer - A::D
The `d` and `f` orbitals do not shield the nucleus charge very effectively. Therefore there is significant reducion 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 (Nb^(3+) = 0.72 Å)` and `Ta(Ta^(3+) = 0.72 Å)` are almost identical due to lanthanide contraction. This is also the reason for the higher ionisation energy of gold than silver.