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The D-And-f-Block Elements

Question
CBSEENCH12011061
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Because of lanthanoid contraction, of elements which of the following elements have nearly same atomic radii ? (Number in the parenthesis are atomic number).

  • Ti (22) and Zr(40)

  • Zr(40) and Nb (41)

  • Zr (40) and Hf (72)

  • Zr (40) and Ta(73)

Solution

C.

Zr (40) and Hf (72)

Because of the lanthanoid contraction Zr (atomic radii 160 pm) and Hf (atomic radii 158 pm) have nearly same atomic radii.
Lanthanoids include the elements from lanthanum La (Z=57) to lutetium Lu(Z =71).Zirconium  Zr (40) belong to the second transition series (4d) and Hf (72) belongs to third transition series (5d). Lanthanoid contraction is associated with the intervention of the 4f orbitals which are filled before the 5d- series of elements starts. The filling of 4f if orbitals before 5d orbitals result in a regular decrease in atomic radii which compensates the expected increases in atomic size with increasing atomic number. As a result of this lanthanoid contraction, the elements of second and third transition series have almost similar atomic radii.

Some More Questions From The d-And-f-Block Elements Chapter

In the series Sc (Z = 21) to Zn(Z = 30), the enthalpy of atomisation of zinc is the lowest i.e., 26, kJ mol. Why?

The E° (M2+/M) value for copper is positive (+ 0.34 V). What is possibility the reason for this? 

How would you account for the irregular variation of ionisation enthalpies (first and second) in the first series of the transition elements?

Why is the highest oxidation state of a metal exhibited in its oxide or fluoride only?

Which is a stronger reducing agent Cr2+ or Fe2+ and why?

Explain why Cu+ ion is not stable in aqueous solutions?

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not?

The outer electronic configuration of copper is 3d10 4s1, yet it is considered transition element. Why?

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