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Friday, 18 March 2016

d and f block elements and their propertites

Objectives:-
1.f-Block elements
2.Introduction to lanthanide
3.Oxidation state
4.lanthanide contraction 
5.Chemical reactivity
6.Introduction of Actinides

7.Comparison  of actinides with lanthanide

Inner transition elements
The elements in which the additional electrons enters
(n-2)f
orbitals are called inner transition elements. The valence shell electronic configuration of these elements can be represented as (n – 2)f0-14(n – 1)d0-1ns2.
4f inner transition metals are known as lanthanide because they come immediately after lanthanum and 5f inner transition metals are known as actinides because they come immediately after actinium.


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Atomic and ionic sizes: The Lanthanide Contraction
 As the atomic number increases, each succeeding element contains one more electron in the 4f orbital and one proton in the nucleus. The 4f electrons are ineffective in screening the outer electrons from the nucleus causing imperfect shielding. As a result, there is a gradual increase in the nucleus attraction for the outer electrons. Consequently gradual decrease in size occur.This is called lanthanide contraction.
Illustrative Example
Explain the cause and two consequences of lanthanide contraction.
Solution:
 The poor shielding effect of f-electrons is cause of lanthanide contraction.
Consequences
There is close resemblance between 4d and 5d transition series.
Ionization energy of 5d transition series is higher than 3d and 4d transition series.Difficulty in separation of lanthanides
Illustrative Example
Why Zr and Hf have almost similar atomic radii?
 Solution:
Zr and Hf have almost similar atomic radii as a consequence of lanthanide contraction due to which their properties becomes similar.
Illustrative Example
Size of trivalent lanthanoid cation decreases with increase in atomic number. Explain.
It is due to poor shielding effect of f-electrons, valance electrons are strongly attracted towards nucleus, therefore, effective nuclear charge increases, hence ionic size decreases.
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Objectives:-1.f-Block parts2.Introduction to rare earth3.Oxidation state4.lanthanide contraction 5.Chemical reactivity 6.Introduction of Actinides 7.Comparison of actinides with rare earth Inner transition parts The elements during which the extra electrons enters 
(n-2)f orbitals square measure referred to as inner transition parts. The valence shell electronic configuration of those parts may be depicted as (n – 2)f0-14(n – 1)d0-1ns2. 4f inner transition metals square measure referred to as rare earth as a result of {they come|they square measureavailable} straight off when metal and 5f inner transition metals are referred to as actinides as a result of they are available straight off when Ac.Atomic and ionic sizes: The rare earth Contraction
because the number will increaseevery succeeding part contains a new negatron within the 4f orbital and onenucleon within the nucleus. The 4f electrons square measure ineffective in screening the outer electrons from the nucleus inflicting imperfect shielding. As a result, there's a gradual increase within the nucleus attraction for the outer electrons. Consequently gradual decrease in size occur.This is referred to as rare earth contraction. Illustrative Example Explain the cause and 2 consequences of rare earth contraction.Solution:The poor shielding result of f-electrons is explanation for rare earth contraction.
Consequences  There is shut alikeness between 4d and 5d transition series.Ionization energy of 5d transition series is over 3d and 4d transition series.Difficulty in separation of lanthanides Illustrative Example Why zirconium and Hf have virtually similar atomic radii? Solution: Zr and Hf have virtually similar atomic radii as a consequence of rare earth contraction as a result of that their properties becomes similar. Illustrative Example Size of power grouping ion decreases with increase in number. Explain. It is as a result of poor shielding result of f-electrons, pelmet electrons square measure powerfully attracted towards nucleus, therefore, effective nuclear charge will increasethence ionic size decreases.
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