CBSE Class 12 Chemistry Transition Elements Notes

CBSE Class 12 Chemistry Revision Transition Elements. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examination.

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D and f block

1. Definitions and examples types of transition series in transition elements

2. Properties (physical and chemical) in transition element

3. Preparation and properties in the transition elements K2Cr2O7, KMnO4

a. Magnetic nature

b. Melting points

c. Alloys formation

d. Interstitial compounds

e. Oxidation states

f. Coloured complexes 

g.Reduction potential 

4. lanthanoids and actinoids with their properties 

5.lanthanoid contraction reason and concequences 

The d-block consisting of Groups 3-12 occupies the large middle section of the periodic table. In these elements the inner d orbitals are progressively filled. The f-block is placed outside at the bottom of the periodic table and in the elements of this block, 4f and5f orbitals are progressively filled. 

--All the transition elements exhibit typical metallic properties such as –high tensile strength, ductility, malleability, thermal and electrical conductivity and metallic character. 

--Their melting and boiling points are high which are attributed to the involvement of (n –1) d electrons resulting into strong inter atomic bonding 

--Successive ionisation enthalpies do not increase as steeply as in the main group elements with increasing atomic number 

--Electronic Configurations of the d-Block Elements 

In general the electronic configuration of these elements is(n-1)d 1–10 n s 1–2.

variation in Atomic and Ionic Sizes of Transition Metals 

In general, ions of the same charge in a given series show progressive decrease in radius with increasing atomic number. This is because the new electron enters a d orbital each time the nuclear charge increases by unity 

Ionisation Enthalpies Due to an increase in nuclear charge which accompanies the filling of the inner d orbitals, there is an increase in ionisation enthalpy along each series of the transition elements from left to right 

. There is the generally expected increasing trend in the values as the effective nuclear charge increases . However, the value of Cr is lower because of the absence of any change in the d configuration and the value for Zn higher because it represents an ionization from the 4s level. The lowest common oxidation state of these metals is +2 

Oxidation States One of the notable features of a transition element is the great variety of oxidation states The elements which give the greatest number of oxidation states occur in or near the middle of the series. Manganese, for example ,exhibits all the oxidation states from +2 to +7. 

Magnetic Properties Many of the transition metal ions are paramagnetic .Paramagnetism arises from the presence of unpaired electrons, each such electron having a magnetic moment associated with its spin angular momentum and orbital angular momentum. For the compounds of the first series of transition metals, the contribution of the orbital angular momentum is effectively quenched and hence is of no significance. For these, the magnetic moment is determined by the number of unpaired electrons and is calculated by using the ‘spin only’ formula ,i.e.,

class_12_chemistry_concept_3

where n is the number of unpaired electrons and μ is the magnetic moment in units of Bohr magneton (BM) 

.Formation of Coloured Ions When an electron from a lower energy d orbital is excited to a higher energy d orbital, the energy of excitation corresponds to the frequency of light absorbed This frequency generally lies in the visible region. The colour observed corresponds to the complementary colour of the light absorbed 

. Formation of Complex Compounds The transition metals form a large number of complex compounds .This is due to the comparatively smaller sizes of the metal ions, their high ionic charges and the availability of d orbitals for bond formation. A few examples are: [Fe(CN)6]3–, [Fe(CN)6]4–,[Cu(NH3)4]2+ and [PtCl4]2–. 

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