NCERT Solutions for Class 12 Chemistry Chapter 4 The d and f Block Elements - Free PDF Download
Chapter 4 Chemistry Class 12 deals with the d and f block of the modern periodic table. The chapter is essential to understand the electronic configuration and the general characteristics of transition elements, oxidization, and chemical reactivity.
For students appearing in the board exams, this chapter is crucial as several essential questions are set from this chapter. In this regard, the Class 12 Chemistry Chapter 4 NCERT solutions come as a great help.
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Important Topics Covered in NCERT Solutions Class 12 Chemistry Chapter 4 The d- and f-block Elements
Students are suggested to go through the following topics and the subsequent sub-topics from NCERT Class 12 Chemistry Chapter 4 thoroughly for their exam preparation.
Position of d-block Elements in the Periodic Table
Position of f-block Elements in the Periodic Table
Electronic Configuration of d-block Elements
General Properties of the d-block Elements or Transition Elements
Transition Elements Important Compounds
Lanthanoids and Actinoids
Applications of d and f-block Elements
The d-and f-Block Elements Chapter at a Glance - Class 12 NCERT Solutions
d-Block Elements
d-block elements are those in which the last electron goes to (n-1) d-orbitals.
General electronic configurations of d-block elements is : ns1-2, (n-1)d1-10
Transition metals have high values of melting and boiling points which are due to the presence of strong metallic bonding in these metals.
Due to lanthanide contraction, atomic radii for the elements of 3rd transition series are almost equal to those for the elements of 2nd transition series.
The values of ionisation energies increase as we move from left to right in each series.
Except for Cu, E°red values for other metals of 1st transition series are negative.
Excepting a few metals, most of the metals show several oxidation states. This is due to the fact that (n-1)d and ns orbitals have almost the same energy.
Transition metal ions which contain partially filled d-orbitals are usually coloured. The colour arises because of d0-d10 transition. Transition metal ions with d0 or d10 configuration
are colourless because d-d transition is not possible in such ions.
Transition metals form interstitial compounds.
Many transition metals and their alloys and compounds act as catalysts in many chemical reactions.
f-Block Elements
The elements in which the last electron enters f-orbital of (n- 2)th shell are called f-block elements. f-block elements are of two types lanthanides and actinides.
General electronic configuration of f-block elements is ns2, (n-1)d0-1, (n-2)f1-14
+ 3 oxidation state (O.S.) is the most stable O.S. of lanthanides.
There is a steady decrease in atomic and ionic (M3+ ions) radii of lanthanides. This steady decrease in atomic and ionic radii is called lanthanide contraction.
Magnetic moment value of lanthanides and actinides is calculated by considering both orbital spin contribution. Μeff value is given by μeff = 4S (S+1)+L(L+1) B.M, here S spin quantum number and L= orbital quantum number
Mischmetal is an important alloy of lanthanides. It contains 90% lanthanides (La= 40%, Ce and other lanthanides= 50%) , Fe = 5% and traces of other elements like C, S, Al, Ca.
The actinide elements lying beyond U (Np-93 to Lw-103) are called trans-uranic or trans-uranium elements.
Unlike lanthanides, actinides show a large number of oxidation states.
Actinides have lower values of ionisation energies.
Most of actinide halides form complex compounds with alkali metal halides. The degree of complex formation for the ions decreases as : M4+ > MO2 2+ > M3+ > MO2+.
Thorium is used in atomic reactors and in the treatment of cancer. Uranium is used as a nuclear fuel. Plutonium is used as a fuel for atomic reactors as well as for making atomic bombs.
d-and f-Block Elements
FAQs on NCERT Solutions for Class 12 Chemistry Chapter 4 The D and F Block Elements
1. What is the general electronic configuration of d-block elements covered in NCERT Solutions for Class 12 Chemistry Chapter 4?
The general electronic configuration of d-block elements is ns1–2 (n–1)d1–10. In these elements, the last electron enters the (n–1)d orbital, resulting in their distinct properties as transition metals.
2. How do the NCERT Solutions for Class 12 Chemistry Chapter 4 explain variable oxidation states in transition elements?
According to NCERT Solutions, transition elements exhibit variable oxidation states because the energies of (n–1)d and ns orbitals are very close. This allows both types of electrons to participate in bonding, resulting in multiple stable oxidation states for elements like iron, manganese, and chromium.
3. Why are most transition metal complexes colored, as per the NCERT Solutions for The d and f Block Elements?
Transition metal complexes are usually colored because of d–d electronic transitions. When visible light is absorbed, electrons can move between split d-orbitals, producing characteristic colors except when the d-orbitals are either empty (d0) or fully filled (d10).
4. In the NCERT Solutions, how is the concept of lanthanide contraction described, and what is its significance?
Lanthanide contraction refers to the steady decrease in atomic and ionic radii of the lanthanide series elements as the atomic number increases. This occurs due to poor shielding effect of 4f electrons. Its significance lies in explaining similar radii between elements of the 2nd and 3rd transition series and affecting chemical properties such as basicity and complex formation.
5. What is the most stable oxidation state of lanthanides according to CBSE Class 12 Chemistry Chapter 4 NCERT Solutions?
The +3 oxidation state is the most stable and common oxidation state for lanthanides, as detailed in Chapter 4 NCERT Solutions. Some lanthanides may exhibit +2 and +4 states, but +3 predominates due to electronic configuration stability.
6. How do the NCERT Solutions justify that the silver atom is considered a transition element despite having a filled d-orbital in its ground state?
Silver (Ag) has a ground state configuration of [Kr] 4d10 5s1 (filled d10), but in its common oxidation state (+1), it forms Ag+ with a 4d10 configuration. However, since it can form compounds with partially filled d-orbitals, it is classified as a transition element as per CBSE guidelines.
7. Explain, using NCERT Solutions, why the enthalpy of atomization of zinc is the lowest among 3d series elements.
Zinc (Zn) has a fully filled d-orbital (3d10 4s2) leading to weak metallic bonding and reduced tendency to form metallic bonds, resulting in the lowest enthalpy of atomization among 3d series transition metals.
8. As per NCERT Solutions, which 3d series transition metal exhibits the largest number of oxidation states, and why?
Manganese (Mn) in the 3d series shows the largest number of oxidation states (from +2 to +7) due to the maximum unpaired electrons in its d-orbitals, which allows easy loss of electrons and access to multiple oxidation states.
9. Why is the E0(M2+/M) value for copper positive, according to the NCERT Solutions for The d and f Block Elements?
The standard electrode potential, E0(Cu2+/Cu), is positive because of the high enthalpy of atomization and high ionization energy of copper. As a result, copper is less likely to lose electrons in aqueous solution, making the reduction reaction favorable (i.e., Cu2+ is more stable than neutral Cu under standard conditions).
10. What practical applications of d and f block elements are highlighted in Class 12 NCERT Solutions?
The NCERT Solutions identify several practical uses for d and f block elements:
- Transition metals: catalysts in industrial reactions (e.g., iron in Haber process).
- Lanthanoids: production of alloys like mischmetal, in optical devices, and as catalysts.
- Actinoids: uranium and plutonium in nuclear reactors, thorium in cancer treatment.
11. How do the NCERT Solutions for Class 12 Chemistry Chapter 4 help clarify misconceptions about the position of lanthanum in the periodic table?
NCERT Solutions clarify that lanthanum (La) is positioned in the d-block as it starts filling the 5d orbital ([Xe] 5d1 6s2), not the f-block, which begins with cerium (Ce). This distinction is crucial for accurate periodic table understanding and often confuses students.
12. In what ways do stepwise explanations in Vedantu NCERT Solutions enhance exam preparation for Chapter 4 d- and f-Block Elements?
Stepwise solutions in Vedantu's NCERT Solutions reinforce:
- Understanding key concepts through logical steps as per CBSE pattern
- Connecting theory with solved examples and diagrams
- Breaking down complex problems into manageable stages for scoring higher marks
13. What is lanthanide contraction, and how does it influence the chemistry of transition elements in NCERT Chapter 4?
Lanthanide contraction is the gradual decrease in size of lanthanides with increasing atomic number. This phenomenon causes elements of the 3rd transition series to have radii similar to those of the 2nd series, affecting trends in basicity, complex formation, and separation of elements.
14. Why are f-block elements positioned below the main periodic table, as explained in NCERT Solutions for Class 12 Chemistry?
The f-block (lanthanides and actinides) is placed below the main table to maintain the table's compact shape and avoid stretching it horizontally. These elements fit between group 2 and 3 according to atomic numbers, but their separate placement aids clarity in periodic trends discussion.
15. How do the NCERT Solutions recommend differentiating between transition elements and inner transition elements for CBSE examinations?
Transition elements (d-block) have partially filled d-orbitals; inner transition elements (f-block) have partially filled f-orbitals. NCERT Solutions guide students to identify them based on electronic configurations and their placement within the periodic table, which is important for CBSE board exams.
