CBSE Class 12 Chemistry D and F Block Exam Notes

CBSE Class 12 Chemistry D and F Block Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Q1.What are d-Block elements?
Ans.These are those elements in which the last electron enter the d-subshell.

Q2.Why are d-block elements called transition elements?
Ans.Because in this block the elements lie between s and p block i.e., between group 12 and group 13.

Q3.Give the general electronic configuration of d-block elements.
Ans.(n – 1)d^1–10 ns^{1– 2}

Q4.Name the 3 series of transition elements.
Ans.(i)3d series
First transition series. Has 10 elements from scandium (Sc) to Zinc (Zn)
(ii)4d series
Second transition series. Has 10 elements from Yttium (Y) to cadmium (Cd)
(iii)5d series
Third transition series. Has 10 elements from Lanthanium (La) to mercury (Hg)

Q5.Which is the most commonly known feature/characteristic of d-block elements.
Ans.It is the presence of un paired electrons in the d-orbitals ; i.e., incompletely set of d-orbitals.

Q6.Why Zn, Hg and Cd often not regarded as transition elements.
Ans.Being the end members of their respective transition series, their configuration is generally given by (n – 1) d¹⁰ ns² i.e., these elements have completely filled d-orbitals and hence do not fulfill the general characteristic of d-block elements which the pressence of incompletely filled d-orbital. Hence are not regarded as transition elements.

Q7.On what grounds you can say that Scandium (Z = 21) is a transition elements but Zn is not?
Ans.Electronic configuration of Sc (Z = 21) 

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹ 

Electronic configuration of Zn (t =30) 

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 

We can say this on the basis of filling of d orbitals. Sc fulfills the general condition of d-block due to presence of incompletely filled d-orbitals (Presence of unpaired electrons) whereas zinc does not as it has completely filled of orbital.

Q8.Why does Ionic size or atomic size decrease in any transition series ?
Ans.As were move left in the transition series the nuclear charge increase by one unit and the additional e^– goes into the inner d-orbital and since d e^–s are poor shielded so they high effective nuclear charge and attracted towards the nucleus due to which decrease in atomic and ionic radius is observed.

Q9.Why do transition metals show variable oxidation states?
Ans.This is because the outer ns electrons also participate with the inner (n – 1)d electrons in bond as their energies are same. And also due to presence of incompletely filled d-orbitals so diff no. of electrons can be lost by atoms.

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