Identify the incorrect statement among the following:
A
Lanthanoid contraction is the accumulation of successive shrinkages.
B
As a result of lanthanoid contraction, the properties of 4d series of the transition elements have no similarities with the 5d series of elements.
C
Shielding power of 4f electrons is quite weak.
D
There is a decrease in the radii of the atoms or ions as one proceeds from La to Lu.
The answer is B.
Solution
There is a steady decrease in the atomic and ionic radii as the atomic number of the lanthanoid elements increases from La to Lu. For every additional proton added to the nucleus, the corresponding electron goes into the 4f subshell. The shape of the f-orbitals is very diffused, so they have a poor shielding effect. The effective nuclear charge therefore increases, which causes a contraction in the size of the electron cloud. This contraction is quite regular; the small successive shrinkages accumulate and the total is known as the lanthanoid contraction. As a consequence, the elements of the 5d series have almost the same radii as the corresponding elements of the 4d series (for example Zr 160 pm and Hf 159 pm), so the 4d and 5d elements are very similar in their properties and are difficult to separate. So the statement that the 4d series has no similarities with the 5d series is incorrect.
ConceptConsequences of lanthanoid contraction
Lanthanoid contraction in past papers
6 questions from this chapter have appeared across 6 exam years.
