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Chapter 8- The d and f Block Elements Interview Questions Answers

Question 1 : Silver atom has completely filled d-orbitals (4d10) in itsground state. How can you say that it is a transition element?

Answer 1 :

Silver (Z = 47) can exhibit +2 oxidation statewherein it will have incompletely filled d-orbitals (4d), hence it is atransition element.

Question 2 : In the series Sc (Z = 21) to Zn (Z = 30), the enthalpy of atomisation ofzinc is the lowest, i.e., 126 kJ mol-1. Why?

Answer 2 :

In the formation of metallic bonds, noelectrons from 3d-orbitals are involved in case of zinc, while in all othermetals of the 3d-series, electrons from the d-orbitals are always involved inthe formation of metallic bonds.

Question 3 : Which of the 3d-series of the transition metals exhibits the largestnumber of oxidation states and why?

Answer 3 :

Manganese (Z = 25), as its atom has themaximum number of unpaired electrons.

Question 4 : The E°(M2+/M) value for copper is positive (+0.34 V). What ispossibly the reason for this? (Hint: consider its high ∆aH° and low∆hydH°)

Answer 4 :

The high energy to transform Cu(s) toCu2+(aq) is not found balanced by its hydrationenergy. Hydration energy and lattice energy of Cu2+ is morethan Cu.

Question 5 : How would you account for the irregular variation of ionisationenthalpies (first and second) in the first series of the transition elements?

Answer 5 :

Irregular variation of ionisation enthalpiesis mainly attributed to varying degree of stability of different 3d –configurations (e.g., d°, d5, d10 are exceptionallystable).

Question 6 : Why is the highest oxidation state of a metal exhibited in its oxide orfluoride only?

Answer 6 :

Because of small size and highelectronegativity oxygen or fluorine can oxidise the metal to its highestoxidation state.

Question 7 : Which is a stronger reducing agent Cr2+ or Fe2+ andwhy?

Answer 7 :

Cr2+ is stronger reducingagent than Fe2+ Reason: d4 → d3 occursin case of Cr2+ to Cr2+. But d6 → d5 occursin case of Fe2+ to Fe2+.
In a medium (like water) d’1 is more stable as compared to d5.

Question 8 : Calculate the ‘spin only’ magnetic moment of M2+(aq) ion(Z = 27).

Answer 8 :

Question 9 : Explain why Cu+ ion is not stable in aqueous solutions?

Answer 9 :

Cu+ in aqueous solutionundergoes disproportionation, i.e.,
2Cu+(aq) → Cu2+(aq) + Cu(s)
The stability of Cu2+(aq) rather than Cu+(aq) isdue to the much more negative ∆hyd H°of Cu2+(aq) thanCu+, which more than compensates for the second ionisation enthalpyof Cu.

Question 10 : Actinoid contraction is greater from element to element than lanthanoidcontraction. Why?

Answer 10 :

The 5f electrons are more effectively shieldedfrom nuclear charge. In other words the 5f electrons themselves provide poorshielding from element to element in the seriest.



Chapter 8- The d and f Block Elements Contributors


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