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The D-And-f-Block Elements

Question

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Actinide cations are coloured? Why?

Solution

The cations of actinides are coloured because of the presence of unpaired electrons. The colour observed depends on the number of impaired electrons. The colours of some cations are given below:

Cation of actinide	U³⁺	Np³⁺	Pu³⁺	Am³⁺
Unpaired electrons	3	4	5	6
Colour observed	Red	Violet	Black violet	Pink

The colour is due to electronic transition within the 5f levels. The electronic transitions of actinides are about ten times more intense than those of lanthanides. The difference is due to difference in 4f and 5f electrons.

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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