CBSE Class 12 Chemistry The d and f Block Elements Assignment

CBSE Class 12 Chemistry The d and f Block Elements Assignment. Students are advised to refer to the attached assignments and practise them regularly. This will help them to identify their weak areas and will help them to score better in examination. Parents should download and give the assignments to their children for practice.

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.
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