d and f Block Elements
Comprehensive guide to transition metals and inner transition elements for CBSE Class 12 students. Master the concepts with detailed explanations, examples, and practice questions.
d and f Block Elements
Introduction to d-Block Elements
The d-block elements are located in the middle of the periodic table, between the s-block and p-block elements. These elements are characterized by the gradual filling of the d-orbitals of the penultimate energy shell.
Definition: Transition Elements
Transition Elements: Elements that have partially filled d-orbitals in their ground state or in any of their oxidation states. By this definition, Zn, Cd, and Hg are not considered transition elements as they have full d10 configuration.
Position in Periodic Table
The d-block elements span from Group 3 to Group 12. They are divided into four series:
- First transition series: Scandium (Sc, 21) to Zinc (Zn, 30)
- Second transition series: Yttrium (Y, 39) to Cadmium (Cd, 48)
- Third transition series: Lanthanum (La, 57), Hafnium (Hf, 72) to Mercury (Hg, 80)
- Fourth transition series: Actinium (Ac, 89) and beyond (incomplete)
Key Characteristics of d-Block Elements
- They are all metals with high melting and boiling points
- They exhibit variable oxidation states
- They form colored compounds
- They have catalytic properties
- They form paramagnetic compounds
- They tend to form complex compounds
Explore d-Block Elements
Select an element to learn more about its properties and characteristics
Chromium (Cr) - Atomic Number 24
Electronic Configuration: [Ar] 3d5 4s1
Common Oxidation States: +2, +3, +6
Properties: Hard, silvery metal with high corrosion resistance. Forms colorful compounds.
Uses: Stainless steel production, chrome plating, dyes and pigments.
Copper (Cu) - Atomic Number 29
Electronic Configuration: [Ar] 3d10 4s1
Common Oxidation States: +1, +2
Properties: Reddish-orange, ductile metal with excellent electrical conductivity.
Uses: Electrical wiring, plumbing, coins, and various alloys like brass and bronze.
Iron (Fe) - Atomic Number 26
Electronic Configuration: [Ar] 3d6 4s2
Common Oxidation States: +2, +3
Properties: Malleable, ductile, silver-gray metal. Most common element on Earth by mass.
Uses: Steel production, magnets, hemoglobin in blood, industrial catalysts.
Zinc (Zn) - Atomic Number 30
Electronic Configuration: [Ar] 3d10 4s2
Common Oxidation States: +2
Properties: Bluish-white, lustrous metal. Fair conductor of electricity.
Uses: Galvanization, brass production, batteries, rubber industry.
Electronic Configuration
The general outer electronic configuration of d-block elements is (n-1)d1-10 ns1-2.
Important Exceptions
Chromium (Cr, Z=24): Expected [Ar] 3d4 4s2, but actual configuration is [Ar] 3d5 4s1 due to extra stability of half-filled orbitals.
Copper (Cu, Z=29): Expected [Ar] 3d9 4s2, but actual configuration is [Ar] 3d10 4s1 due to extra stability of fully-filled d-orbitals.
| Series | Elements | Outer Orbital | Number of Elements |
|---|---|---|---|
| First Transition | Sc (21) to Zn (30) | 3d | 10 |
| Second Transition | Y (39) to Cd (48) | 4d | 10 |
| Third Transition | La (57), Hf (72) to Hg (80) | 5d | 10 |
Note:
The anomalous electronic configurations of Chromium and Copper are due to the extra stability associated with half-filled and completely filled subshells. This stability comes from the symmetrical distribution of electrons and exchange energy.
Key Points to Remember
- The (n-1)d orbitals are filled progressively across each series
- The 4s orbital is filled before the 3d orbitals in the first transition series
- Half-filled (d5) and fully-filled (d10) configurations are exceptionally stable
- The electronic configuration determines the magnetic properties and oxidation states
Properties & Trends
Atomic Radii
Decreases from left to right across a period due to poor shielding of d-electrons. The decrease is more gradual compared to p-block elements.
Ionization Enthalpy
Increases gradually along the period due to increasing nuclear charge. The values are higher than s-block but lower than p-block elements.
Oxidation States
Show variable oxidation states due to similar energies of (n-1)d and ns orbitals. The highest oxidation state is often equal to the sum of s and d electrons.
Magnetic Properties
Most are paramagnetic due to unpaired electrons. Magnetic moment μ = √[n(n+2)] BM, where n is the number of unpaired electrons.
Catalytic Properties
Many act as catalysts due to variable oxidation states and surface adsorption. Examples: Fe in Haber's process, V₂O₅ in Contact process.
Formation of Colored Ions
Due to d-d transition where electrons absorb visible light and jump to higher orbitals. The color depends on the nature of the ligand and the metal ion.
Alloy Formation
Transition metals form alloys readily due to similar atomic sizes. Examples: Stainless steel (Fe, Cr, Ni), Brass (Cu, Zn), Bronze (Cu, Sn).
Interstitial Compounds
Formed when small atoms like H, C, N occupy interstitial sites in the crystal lattice. These compounds are hard, have high melting points, and retain metallic conductivity.
Memory Aid: Spectrochemical Series
I Can Barely Operate New Complex Machines Very Carefully
I⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O < NCS⁻ < NH₃ < en < NO₂⁻ < CN⁻ < CO
(Weak field ligands to strong field ligands)
Important Trends
- Melting and boiling points first increase, then decrease across a series
- Density increases down the group and across the period
- Atomic sizes of elements in the second and third transition series are almost identical due to lanthanoid contraction
- The +2 and +3 oxidation states are most common for the first transition series
- Higher oxidation states are more stable for heavier elements
Important Compounds
Potassium Dichromate (K₂Cr₂O₇)
Preparation: From chromite ore (FeCr₂O₄) through fusion with Na₂CO₃ in excess of air.
Properties: Orange crystalline compound, powerful oxidizing agent in acidic medium:
Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O
Uses: In tanning leather, as an oxidant in organic synthesis, and as a primary standard in volumetric analysis.
Potassium Permanganate (KMnO₄)
Preparation: From pyrolusite ore (MnO₂) by fusion with KOH in presence of O₂ followed by electrolytic oxidation.
Properties: Purple crystalline compound, oxidizing agent whose action depends on pH:
Acidic: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O
Neutral: MnO₄⁻ + 2H₂O + 3e⁻ → MnO₂ + 4OH⁻
Uses: As an oxidant, disinfectant, and for bleaching.
Ferrous Sulfate (FeSO₄·7H₂O)
Preparation: By the action of dilute H₂SO₄ on iron.
Properties: Green crystalline solid. On heating, it loses water of crystallization and decomposes:
2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
Uses: In the manufacture of inks, in wool dyeing, and as a reducing agent.
Copper Sulfate (CuSO₄·5H₂O)
Preparation: By the action of hot concentrated H₂SO₄ on copper.
Properties: Blue crystalline solid. On heating, it loses water of crystallization and becomes white.
CuSO₄·5H₂O → CuSO₄ + 5H₂O (on heating)
Uses: In electroplating, as a fungicide, and in the preparation of other copper compounds.
Other Important Compounds
- Silver Nitrate (AgNO₃): Used in photography, silver plating, and as a laboratory reagent
- Mercuric Chloride (HgCl₂): Used as a disinfectant and preservative
- Zinc Oxide (ZnO): Used in paints, ointments, and as a semiconductor
- Potassium Ferrocyanide (K₄[Fe(CN)₆]): Used in dyeing, printing, and as a laboratory reagent
- Titanium Dioxide (TiO₂): Used as a white pigment in paints, plastics, and paper
f-Block Elements
The f-block elements are placed at the bottom of the periodic table and have their valence electrons entering the f-orbitals. They are called inner transition elements.
Lanthanoid Contraction
Lanthanoid Contraction: The steady decrease in atomic and ionic radii from Cerium (Ce) to Lutetium (Lu) due to poor shielding effect of 4f electrons. This results in similar atomic sizes of elements in the second and third transition series (e.g., Zr and Hf, Nb and Ta).
| Property | Lanthanoids | Actinoids |
|---|---|---|
| Configuration | [Xe] 4f1-14 5d0-1 6s2 | [Rn] 5f1-14 6d0-1 7s2 |
| Common Oxidation State | +3 | +3 (but show wide variety) |
| Radioactivity | Only Pm is radioactive | All are radioactive |
| Binding Energy | 4f orbitals have higher binding energy | 5f orbitals have lower binding energy |
| Chemistry | Quite similar to each other | Individualistic for each element |
Note:
Actinoids show a wider range of oxidation states than lanthanoids because the 5f, 6d, and 7s levels are of comparable energies. This allows for greater flexibility in bonding.
Applications of f-Block Elements
- Lanthanoids: Used in production of strong permanent magnets (Nd₂Fe₁₄B), phosphors in color televisions, and catalysts in petroleum refining
- Actinoids: Uranium and plutonium are used as nuclear fuels, americium is used in smoke detectors
- Mixed oxides: Lanthanoid oxides are used in glass polishing and as catalysts
- Cerium: Used in self-cleaning ovens and as a catalytic converter in vehicles
- Thorium: Used in incandescent gas mantles and as a nuclear fuel
Coordination Compounds
Coordination compounds are compounds in which a central metal atom or ion is bonded to a fixed number of ions or molecules.
Key Terms
- Central atom/ion: Usually a transition metal ion
- Ligands: Ions or molecules bound to the central metal atom
- Coordination number: Number of ligand atoms directly bonded to the metal
- Coordination sphere: Central metal ion and its ligands
- Oxidation number: The charge the central atom would carry if all ligands were removed
Valence Bond Theory
Explains geometry based on hybridization of metal orbitals. Example: [Ni(CN)₄]²⁻ is square planar (dsp² hybridization) and diamagnetic.
Crystal Field Theory
Explains color and magnetic properties based on splitting of d-orbitals in the presence of ligands.
Isomerism
Coordination compounds show structural isomerism (ionization, coordination) and stereoisomerism (geometrical, optical).
Example: Tetraamminecopper(II) Ion
Cu²⁺ + 4NH₃ → [Cu(NH₃)₄]²⁺ (deep blue complex)
Importance of Coordination Compounds
- Biological importance: Hemoglobin (Fe), chlorophyll (Mg), vitamin B₁₂ (Co)
- Industrial applications: Catalysts, electroplating, photography
- Medicinal uses: Cis-platin as anticancer drug, EDTA for lead poisoning
- Analytical chemistry: Qualitative and quantitative analysis
- Water softening: Removal of calcium and magnesium ions
Previous Year Questions
CBSE 2023
Q: Write the electronic configuration of Fe²⁺ and Mn³⁺ ions.
Solution: Fe²⁺: [Ar] 3d⁶, Mn³⁺: [Ar] 3d⁴
CBSE 2022
Q: Why is [NiCl₄]²⁻ paramagnetic while [Ni(CN)₄]²⁻ is diamagnetic?
Solution: In [NiCl₄]²⁻, Cl⁻ is a weak field ligand resulting in two unpaired electrons (paramagnetic). In [Ni(CN)₄]²⁻, CN⁻ is a strong field ligand pairing all electrons (diamagnetic).
CBSE 2021
Q: Account for the following: (i) Transition metals show variable oxidation states. (ii) Zr and Hf have almost similar atomic radii.
Solution: (i) Due to small energy difference between (n-1)d and ns orbitals. (ii) Due to Lanthanoid Contraction which causes similar atomic sizes.
CBSE 2020
Q: Explain why transition metals and their compounds act as catalysts.
Solution: Transition metals and their compounds act as catalysts due to:
- Variable oxidation states
- Ability to form unstable intermediate compounds
- Providing large surface area for adsorption
CBSE 2019
Q: What is lanthanoid contraction? What are the consequences of lanthanoid contraction?
Solution: Lanthanoid contraction is the gradual decrease in atomic and ionic radii of lanthanoids with increasing atomic number. Consequences include:
- Similar atomic sizes of elements in the second and third transition series
- Difficulty in separation of lanthanoids due to similar properties
- Basicity differences among lanthanoids
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