d & f Block Elements Part - 1 | Class 12th

Chapter - 8

d & f – Block Elements

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  ü  General Introduction

  ü  Electronic configuration

  ü  Characteristics of transition metals

  ü  General trends in properties

Ø  Metallic character

Ø  Ionization in enthalpy

Ø  Oxidation states

Ø  Ion radii

Ø  Colour

Ø  Catalyst property

Ø  Magnetic properties

  ü  Preparation & properties

Ø  Potassium dichromate

Ø  Potassium permanganate

  ü  Interstitial compounds

  ü  Alloy formation

  ü  Lanthanoids

Ø  Electronic configuration

Ø  Oxidation state

Ø  Chemical reactivity

Ø  Lanthanoid contraction

  ü  Actinoids

Ø  Electronic configuration

Ø  Oxidation state

  ü  Introduction:

·   The elements lying in the middle of periodic table belonging to groups 3 to 12 are known as d – block elements.

·   The elements in which the last electron enters into the d-orbitals of the penultimate shell i.e. (n–1) d where n is the last shell are called d-block elements.

·   They are placed in between s-block and p-block elements.

·   They show a regular transition from the highly electropositive metals of s-block elements to the less electropositive p-block elements. So, they are called transition elements.

Ø  Transition elements

·   A transition element is defined as the one which has incompletely filled d orbitals in its ground state or in any one of its oxidation states.

·   Zinc, cadmium, mercury are not regarded as transition metals due to completely filled d – orbital in both atomic and ionic state.

·   The four series of transition element are:  

    F First transition series                    Sc₂₁ to Zn₃₀

    F Second transition series                     Y₃₉ to Cd₄₈

    F Third transition series                      La₅₇, Hf₇₂ to Hg₈₀

    F                           Fourth transition series                    Ac₈₉, Rf₁₀₄ onwards (incomplete)

Ø  Electronic configuration: General outer electronic configuration of d-block elements is (n-1) d^1-10 ns^1-2. There is only a small difference in energy between (n-1)d orbital and ns orbital. So in some cases ns electrons are also transferred to (n-1)d level.

·   The electronic configurations of Cr and Cu in the 3d series show some exceptions.

₂₄Cr – [Ar] 3d⁵ 4s¹

₂₉Cu – [Ar] 3d¹⁰ 4s¹

This is due to the extra stability of half-filled and completely-filled electronic configurations. (d⁵ or d¹⁰).

  ü  General Characteristics of transition element:

·   Atomic Radii: The atomic radii decrease from Sc to Cr because the effective nuclear charge increases. The atomic size of Fe, Co, Ni is almost same because the attraction due to increase in nuclear charge is cancelled by the repulsion because of increase in shielding effect. Cu and Zn have bigger size because the shielding effect increases and electron electron repulsions repulsion increases.

·   Ionic Radii: The atomic and ionic radii of 2^nd and 3^rd row transition metals are quite similar. This is due to the Lanthanoid contraction. In between the 2^nd and 3^rd row transition elements, 4f electrons are present. The 4f electrons have very poor shielding effect and as a result the atomic and ionic radii of Lanthanoid decrease from left to right (Lanthanoid contraction).