Chapter 8 The d and f Block Elements Solutions
Question - 1 : - Silver atom has completely filled┬аd┬аorbitals (4d10) in its ground state. How can you saythat it is a transition element?
Answer - 1 : -
Ag has a completely filled 4d┬аorbital (4d10┬а5s1) in its ground state. Now, silverdisplays two oxidation states (+1 and +2). In the +1 oxidation state, anelectron is removed from the┬аs-orboital.However, in the +2 oxidation state, an electron is removed from the┬аd-orbital. Thus, the┬аd-orbital now becomes incomplete (4d9).Hence, it is a transition element.
Question - 2 : - Silver atom has completely filled d-orbitals (4d10) in itsground state. How can you say that it is a transition element?
Answer - 2 : -
Silver (Z = 47) can exhibit +2 oxidation statewherein it will have incompletely filled d-orbitals (4d), hence it is atransition element.
Question - 3 : - 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 - 3 : -
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 - 4 : - Which of the 3d-series of the transition metals exhibits the largestnumber of oxidation states and why?
Answer - 4 : -
Manganese (Z = 25), as its atom has themaximum number of unpaired electrons.
Question - 5 : - The E┬░(M2+/M) value for copper is positive (+0.34 V). What ispossibly the reason for this? (Hint: consider its high тИЖaH┬░ and lowтИЖhydH┬░)
Answer - 5 : -
The high energy to transform Cu(s)┬аtoCu2+(aq)┬аis not found balanced by its hydrationenergy. Hydration energy and lattice energy of Cu2+┬аis morethan Cu.
Question - 6 : - How would you account for the irregular variation of ionisationenthalpies (first and second) in the first series of the transition elements?
Answer - 6 : -
Irregular variation of ionisation enthalpiesis mainly attributed to varying degree of stability of different 3d тАУconfigurations (e.g., d┬░, d5, d10┬аare exceptionallystable).
Question - 7 : - Why is the highest oxidation state of a metal exhibited in its oxide orfluoride only?
Answer - 7 : -
Because of small size and highelectronegativity oxygen or fluorine can oxidise the metal to its highestoxidation state.
Question - 8 : - Which is a stronger reducing agent Cr2+┬аor Fe2+┬аandwhy?
Answer - 8 : -
Cr2+┬аis stronger reducingagent than Fe2+┬аReason: d4┬атЖТ d3┬аoccursin case of Cr2+┬аto Cr2+. But d6┬атЖТ d5┬аoccursin case of Fe2+┬аto Fe2+.
In a medium (like water) dтАЩ1 is more stable as compared to d5.
Question - 9 : - Calculate the тАШspin onlyтАЩ magnetic moment of M2+(aq)┬аion(Z = 27).
Answer - 9 : - 
Question - 10 : - Explain why Cu+┬аion is not stable in aqueous solutions?
Answer - 10 : -
Cu+┬аin aqueous solutionundergoes disproportionation, i.e.,
2Cu+(aq)┬атЖТ Cu2+(aq)┬а+ Cu(s)
The stability of Cu2+(aq)┬аrather than Cu+(aq)┬аisdue to the much more negative тИЖhyd┬аH┬░of Cu2+(aq)┬аthanCu+, which more than compensates for the second ionisation enthalpyof Cu.