CBSE Class 12 Chemistry The d and f Block Elements Assignment

Q.1-Explain briefly how +2 oxidation states becomes more and more stable in the first half of the first row transition elements with increasing atomic number.

Ans.1-In M2+ ions, 3d-orbitals get occupied gradually as the atomic number increases. Since, the number of empty d-orbitals decreases, the stability of cations increases from Sc2+ to Mn2+ .Mn2+ is most stable as all d-orbitals are singly occupied.

Q.2- Explain why transition elements have many irregularities in their electronic configurations?

Ans.2-In the transition elements, there is a little difference in the energy of (n-1) d-orbitals and nsorbitals. Thus, incoming electron can occupy either of shell. Hence, transition elements exhibit many irregularities in their electronic configurations.

Q.3-What are different oxidation states exhibited by Lanthanides?

Ans.3-The common stable oxidation state of lanthanides is +3.However some members also show oxidation states of +2 & +4.

Q.4-How is the variability in oxidation states of transition metals different from that of the non-transition metals? Illustrate with examples.

Ans.4-The transition elements use its (n-1)d, ns and np orbital and the successive oxidation states differ by unity. For example, Mn shows all the oxidation states from +2 to +7. On other hand non transition elements use its ns, np and nd orbitals and the successive oxidation states differ by two units e.g. Sn2+, Sn4+ etc.

Q.5- Why do transition elements show variable oxidation states?

Ans.5- The transition elements show variable oxidation state due to small energy difference between (n-1) d &ns orbital as a result both (n-1)d &ns electrons take part in bond formation.

Q.6-Why are Mn2+ compounds more stable than Fe2+ compounds towards oxidation to +3 state?

Ans.6-The electronic configuration of Mn2+ is [Ar] 3d5, i.e. all five d-orbitals are singly occupied. Thus this is stable electronic configuration and further loss of electron requires high energy .on other hand side the electronic configuration of Fe2+is [Ar] 3d6, i.e. Loss of one electron requires low energy.

Q.7-To what extend do the electronic configuration decide the stability of oxidation state in the first series of the transition elements? Illustrate your answer with an example.

Ans.7-In a transition series, the oxidation state which lead to exactly half filled or completely filled orbitals are more stable.e.g. the electronic configuration of Feis [Ar] 3d6 ,4s2. It shows various oxidation state but Fe(III) is more stable than Fe(II).

Q.8- Which metal in the first series of transition metals exhibits +1 oxidation state most frequently and why?

Ans.8- Copper with configuration [Ar] 3d10 4s1 exhibits +1 oxidation state. Copper loses 4s1 electron easily and achieved a stable configuration 3d10 by forming Cu+.

Q.9- What are inner transition elements?

Ans.9- The f-block elements in which the last electron accommodated on (n-2) f-subshell are called inner transition elements. These include atomic numbers 58 to 71 and from 90 to 103.

Q.10- The paramagnetic character in 3d-transition series elements increases upto Mn and then decreases. Explain why?

Ans.10- In the 3d-transition series as we move from Sc (21) to Mn (25) the number of unpaired electrons increases and hence paramagnetic character increases. After Mn, the pairing of electrons in the d-orbital starts and the number of unpaired electrons decreases and hence, paramagnetic character decreases.

Q.11- Comment on the statement that elements of the first transition series possess many properties different from those of heavier transition metal

Ans.11-The following points justify that the given statement is true:-