The d-block of the periodic table includes elements from groups 3 to 12. These elements fill up the d orbitals across the four long rows in the table. On the other hand, the f-block contains elements where the 4f and 5f orbitals are filled up. These elements are placed separately at the bottom of the table. We commonly call the elements in the d-block "transition metals" and the ones in the f-block "inner transition metals."
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Class 12 Chemistry Chapters List:- JEE & NEET Revision Notes
Transition elements have comparable energies of the ns and (n−1)d orbitals, allowing electrons from both orbitals to participate in chemical bonding. As a result, they exhibit multiple oxidation states depending on the compound and reaction conditions.
After completing d- and f-Block Elements, continue with Coordination Compounds. The concepts of electronic configuration, oxidation states, magnetic properties, and complex formation learned in this chapter provide a strong foundation for understanding coordination chemistry.
Most transition metal ions contain partially filled d-orbitals. When light is absorbed, electrons undergo d-d electronic transitions, resulting in the appearance of characteristic colours. Ions with d⁰ or d¹⁰ configurations are generally colourless.
Lanthanoid contraction refers to the gradual decrease in the ionic and atomic radii of lanthanoids from lanthanum to lutetium due to poor shielding by 4f electrons. It explains similarities in the properties of transition elements and affects complex formation, basicity, and atomic size trends.
The most important topics include electronic configurations, variable oxidation states, magnetic properties, coloured compounds, lanthanoid contraction, and the properties of potassium permanganate (KMnO₄) and potassium dichromate (K₂Cr₂O₇). These concepts are frequently tested in both objective and conceptual questions.
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Class 12 Chemistry Chapter 4: d- and f-block Elements
The d- and f-Block Elements chapter introduces transition elements and inner transition elements, highlighting their unique electronic configurations, oxidation states, magnetic properties, coloured compounds, catalytic behaviour, and complex formation. It also explains the characteristics of lanthanoids and actinoids, including the lanthanoid contraction and its consequences. Since this chapter involves conceptual learning, periodic trends, and application-based questions, it carries significant weightage in JEE Main, JEE Advanced, NEET, and CBSE Board examinations.
At ALLEN, Class 12 Chemistry Chapter 4: d and f blocks element study materials are prepared by expert chemistry faculty to simplify d- and f-block Elements through concise theory, concept-based explanations, important trends, electronic configurations, comparison tables, previous years' question (PYQ) analysis, and exam-oriented revision tips. These notes help students revise important exceptions, periodic trends, and conceptual facts efficiently before examinations.
1.0Chapter Snapshot
Parameter
Details
Difficulty Level
Moderate
JEE Main Weightage
High (Generally 1–2 Questions)
JEE Advanced Weightage
High (2–4 Integrated Concepts)
Key Concepts Covered
Transition Elements, Oxidation States, Magnetic Properties, Lanthanoids, Actinoids, Lanthanoid Contraction
The d-block occupies the central portion of the periodic table, situated between the s-block and p-block elements. Within this section, the d-orbitals of the penultimate energy level of atoms accept electrons, leading to the emergence of four rows of transition metals: the 3d, 4d, 5d, and 6d series.
2.0Electronic Configuration
The electronic configuration of d-block elements typically follows the pattern(n – 1)d1-10ns0 –2.
However elements such as Zn, Cd, Hg, etc., which have completely filled d-orbitals [(n – 1)d10], are considered d-block elements but not transition metals.
3.0Properties of d Block
Transition elements, also known as transition metals, exhibit several general properties:
Variable Oxidation States: Transition metals can exist in multiple oxidation states due to the availability of d-electrons that can be easily lost or gained in chemical reactions.
Formation of Colored Compounds: Many transition metal compounds display vivid colors due to d-electrons transition, which can emit specific wavelengths of light.
Formation of Complex Ions: Transition metals readily form complex ions by coordinating with ligands, molecules, or ions that donate electron pairs to the metal ion.
Catalytic Activity: Transition metals often act as catalysts in various chemical reactions due to their ability to change oxidation state during the reaction process.
Paramagnetism: Transition metal ions with unpaired electrons are often paramagnetic, attracting them to an external magnetic field.
High Melting and Boiling Points: Transition metals typically have high melting and boiling points due to strong metallic bonding resulting from d-electrons.
Malleability and Ductility: Transition metals are generally malleable and ductile, hammered into thin sheets or drawn into wires without breaking.
Density: Transition metals tend to have high densities compared to other elements.
Formation of Alloys: Transition metals readily form alloys with other metals, resulting in materials with enhanced properties such as strength and corrosion resistance.
4.0Importance in Catalysis
Transition metals are essential catalysts in various chemical reactions due to their ability to transition between different oxidation states. In given examples, transition metals accelerate reactions by providing active surfaces for reactants, enhancing reaction rates and efficiency.
Haber’s Process: Iron catalyzes ammonia synthesis by providing a surface for nitrogen and hydrogen molecules to react and produce ammonia efficiently.
Hydrogenation of Alkenes: Nickel catalyzes the hydrogenation of alkenes into alkanes by adsorbing both the alkene and hydrogen molecules, facilitating their addition reaction.
Contact Process: Vanadium(V) oxide acts as a catalyst in sulfuric acid production, speeding up the oxidation of sulfur dioxide to sulfur trioxide by atmospheric oxygen.
5.0Compounds of Transition Elements
Important Compounds of Transition Elements are listed below:
Potassium Dichromate (K2Cr2O7) is used in the leather industry and as an oxidizing agent in azo compound preparation due to its potent oxidizing capabilities.
Potassium Permanganate (KMnO4) is a strong oxidant employed in organic chemistry, textile bleaching, and oil decolorization. It is characterized by its striking purple color and varying magnetic properties with temperature.
Ferrous Sulfate (FeSO4): Widely used in medicine and agriculture, it is an iron supplement for treating anemia and a soil amendment for enhancing crop yields by correcting iron deficiencies in plants.
Cobalt Chloride (CoCl2): Noted for its blue color, cobalt chloride functions as a humidity indicator in desiccants. It undergoes reversible hydration reactions to change color in response to varying humidity levels.
6.0The Inner Transition Elements (f-block)
The f-block elements comprise two series of elements: the Lanthanides, also known as Lanthanons, and the Actinides, also known as Actanones. These elements encompass 28 elements from atomic number 58 to 71 and from atomic number 90 to 103, arranged in two horizontal rows below the main body of the Periodic Table.
The f-block elements are those in which the f orbitals are being filled with electrons. These elements typically have electrons filling the f orbitals, ranging from 1 to 14, alongside 0 to 1 electron in the d orbital of the penultimate energy level and the outermost orbital.
f-block elements are categorized into two series: lanthanides and actinides. This block of elements is commonly referred to as inner transition metals due to its role in bridging the gap between the s block and d block elements in the periodic table, providing a transition within the 6th and 7th rows.
These two series within the f-block correspond to the filling of the 4f and 5f orbitals. The 4f series spans from Ce to Lu and encompasses 14 elements, while the 5f series ranges from Th to Lw and also comprises 14 elements. These elements are characterized by the gradual filling of the f orbitals within each series.
Properties of Lanthanides
Soft, silvery-white metals.
Tend to dull and lose brightness when exposed to air.
Melting points range from 1000 K to 1200 K (except Samarium, 1623K).
Good conductors of heat and electricity.
Mostly non-radioactive, except promethium.
Exhibit lanthanoid contraction, with decreasing atomic and ionic radii from lanthanum to lutetium.
Properties of Actinides
Silvery appearance.
Radioactive nature.
Highly reactive, mainly when finely divided.
Exhibit actinoid contraction, with decreasing atomic and ionic radii from Actinium to Lawrencium.
Predominantly exhibit an oxidation state of +3, although higher oxidation states are common in the first half of the series.
7.0Exceptions in d-block and f-block Elements
Chromium (Cr) and Copper (Cu): Anomalies in electron configuration where Cr is [Ar] 3d5 4s1 and Cu is [Ar] 3d10 4s1, due to stability gained by half-filled (Cr) and fully-filled (Cu) d orbitals.
Lanthanum (La) and Actinium (Ac): Their electron configurations deviate from expected patterns due to small energy differences between 5d and 4f orbitals, resulting in [Xe] 5d1 6s2 for La and [Rn] 6d1 7s2 for Ac.
Lanthanide Contraction: Refers to the unexpected decrease in atomic and ionic radii in the lanthanide series due to poor shielding of 4f electrons, causing increased nuclear attraction on outer electrons.
These exceptions highlight the intricacies of electron behavior in transition metals and inner transition metals, deviating from the expected Aufbau principle.
8.0Comparison of d and f block Elements
Property
d-Block Elements
f-Block Elements
Location in Periodic Table
Middle
Bottom and Inner Transition
Electron Configuration
[Noble Gas] ns1-2 (n–1) d1-10
[Noble Gas] (n–2) f1-14 (n–1)d0-1ns2
Physical State
Mostly solid at room temperature
Primarily solid
Magnetic Behavior
Paramagnetic or diamagnetic
Paramagnetic
Radioactivity
Mostly stable
Many are radioactive
Occurrence in Nature
Abundant in Earth’s crust
Rare in Earth’s crust
1.0Learning Outcomes
After completing these revision notes, you will be able to:
Differentiate between transition elements and inner transition elements.
Write the electronic configurations of d-block and f-block elements.
Explain variable oxidation states and their trends.
Understand magnetic properties based on unpaired electrons.
Explain the origin of colour in transition metal compounds.
Describe catalytic activity and complex formation in transition elements.
Understand the lanthanoid contraction and its consequences.
Compare the properties of lanthanoids and actinoids.
2.0Quick Revision Checklist
Must-Revise Concepts
Position of d-Block Elements
Transition Elements
Electronic Configuration
General Characteristics
Variable Oxidation States
Atomic and Ionic Radii
Ionisation Enthalpy
Magnetic Properties
Coloured Ions
Catalytic Properties
Complex Formation
Interstitial Compounds
Alloy Formation
Potassium Dichromate
Potassium Permanganate
Lanthanoids
Lanthanoid Contraction
Consequences of Lanthanoid Contraction
Actinoids
Oxidation States of Actinoids
Comparison of Lanthanoids and Actinoids
Formula & Calculation Checklist
Revise the following concepts and relationships before the examination.
Electronic Configuration of d-Block Elements
Electronic Configuration of Lanthanoids
Electronic Configuration of Actinoids
Spin-Only Magnetic Moment Formula
Number of Unpaired Electrons
Oxidation State Trends
Lanthanoid Contraction
Crystal Field Concept (Basic Understanding)
Stability of Oxidation States
Colour Due to d-d Transitions
Magnetic Behaviour Classification
Complex Formation Tendency
3.0High Weightage Topics
Topic
Key Theoretical Focus
Transition Elements
Electronic configuration and characteristic properties
Variable Oxidation States
Stability and trends across the series
Magnetic Properties
Paramagnetism, diamagnetism, and spin-only magnetic moment
Coloured Compounds
Origin of colour due to d-d electronic transitions
Catalytic Properties
Role of transition metals and their compounds as catalysts
Lanthanoid Contraction
Causes, trends, and important consequences
Lanthanoids & Actinoids
Electronic configuration, oxidation states, and comparative properties
4.0Formula Handbook
The following concepts and relationships are essential for revising d- and f-Block Elements for JEE Main, JEE Advanced, NEET, and CBSE examinations.
5.0Common Mistakes & Exam Tips
This chapter is highly conceptual and requires careful memorization of periodic trends, exceptions, and characteristic properties.
Common Mistake
Exam Tip
Confusing d-block elements with transition elements
Remember that every transition element belongs to the d-block, but not every d-block element is a transition element.
Memorizing electronic configurations without exceptions
Pay special attention to exceptions like Cr and Cu, which are frequently tested.
Confusing lanthanoid contraction with atomic size trends
Revise the cause and consequences of lanthanoid contraction separately.
Forgetting oxidation state trends
Practice oxidation states of important transition metals such as Mn, Fe, Cr, and Cu.
Incorrect calculation of magnetic moment
First determine the number of unpaired electrons, then apply the spin-only formula.
Confusing colourless and coloured ions
Colour depends on partially filled d-orbitals; d⁰ and d¹⁰ ions are generally colourless.
Ignoring NCERT reactions
Revise the preparation and properties of KMnO₄ and K₂Cr₂O₇ thoroughly.
Mixing up lanthanoids and actinoids
Compare their oxidation states, radioactivity, and chemical reactivity using a summary table.
6.0ALLEN Expert Tips
Memorize the electronic configurations of important transition elements along with their common exceptions.
Revise the trends in atomic radius, ionisation enthalpy, oxidation state, and magnetic behaviour together.
Prepare separate notes for the properties and reactions of potassium permanganate (KMnO₄) and potassium dichromate (K₂Cr₂O₇).
Learn the causes and consequences of lanthanoid contraction, as they are frequently asked in board and entrance examinations.
Solve conceptual questions based on coloured ions, magnetic properties, and catalytic behaviour.
Focus on NCERT tables and comparison charts for lanthanoids and actinoids.
Revise characteristic properties through flowcharts rather than isolated facts.
Solve Previous Years' Questions to identify recurring conceptual patterns.
7.0PYQ Trend Analysis
d- and f-Block Elements is a theory-oriented chapter that consistently contributes conceptual questions in JEE Main, JEE Advanced, NEET, and CBSE examinations. Questions commonly focus on electronic configurations, oxidation states, magnetic properties, lanthanoid contraction, and the properties of important compounds such as potassium permanganate and potassium dichromate.
Note: The trend below is based on the analysis of previous years' JEE Main and JEE Advanced question papers. The exact number of questions may vary each year.
Topic
Questions Asked (Last 5 Years)
Average Difficulty
Electronic Configuration
1–2
Easy
Oxidation States
1–2
Moderate
Magnetic Properties
1–2
Moderate
Coloured Compounds
1
Easy
KMnO₄ & K₂Cr₂O₇
1–2
Moderate
Lanthanoid Contraction
1–2
Moderate
Lanthanoids & Actinoids
1–2
Moderate
8.0Most Common Question Types
Question Type
What is Commonly Asked?
Electronic Configuration Questions
Writing configurations and identifying exceptions in transition elements
Conceptual MCQs
Variable oxidation states, coloured ions, catalytic behaviour, and alloy formation
Magnetic Property Questions
Calculating magnetic moment and identifying paramagnetic or diamagnetic species
Lanthanoid Contraction Questions
Causes, effects, and applications of lanthanoid contraction
Compound-Based Questions
Properties, preparation, and uses of KMnO₄ and K₂Cr₂O₇
Assertion & Reason Questions
Transition element characteristics, lanthanoid properties, and oxidation states
Comparison Questions
Differences between transition elements, lanthanoids, and actinoids
9.0Smart Revision Plan
Revise this chapter in the following sequence for better retention and conceptual clarity:
Electronic Configuration of d- and f-Block Elements
General Characteristics of Transition Elements
Variable Oxidation States and Magnetic Properties
Coloured Compounds, Catalytic Behaviour, and Complex Formation
