D and F Block Elements | Class 12 Chemistry | Quick Revision

**Channel:** Sourabh Raina

**Subject:** Chemistry

**Class:** 12th

**Chapter:** D & F Block Elements

**Topic:** D & F Block Elements Revision

Summary

This video provides a quick revision of the D and F block elements for Class 12 Chemistry, covering their electronic configuration, physical properties (size, enthalpy of atomization, ionization enthalpy), oxidation states, metallic character, standard electrode potential, magnetic properties, complex formation, alloy formation, and detailed information on the F-block elements (Lanthanoids and Actinoids), including their differences. It also touches upon specific compounds like Potassium Dichromate and Potassium Permanganate, and the applications of transition elements.

Key Takeaways

* **D-Block Elements (Transition Elements):** Characterized by the filling of (n-1)d orbitals. They exhibit a wide range of physical and chemical properties due to the presence of unpaired electrons in d-orbitals.

* **Physical Properties of D-Block:** Generally have high melting and boiling points, are dense, and possess good metallic character. Enthalpy of atomization is generally high due to strong interatomic metallic bonds.

* **Ionization Enthalpy:** Generally increases across a period but shows irregularities due to complex electron configurations.

* **Oxidation States:** Exhibit variable oxidation states due to the close energy of (n-1)d and ns electrons.

* **Standard Electrode Potential (E°):** The trend in E° values for M$^{n+}$/M systems is complex and influenced by various factors like sublimation, ionization, and hydration enthalpies.

* **Magnetic Properties:** Most D-block compounds are paramagnetic due to the presence of unpaired electrons.

* **Complex Formation:** Transition metal ions readily form complex compounds due to their small size, high charge density, and availability of vacant d-orbitals.

* **Alloy Formation:** Transition metals form alloys with other metals due to their similar atomic sizes and metallic bonding.

* **F-Block Elements:** Divided into Lanthanoids and Actinoids, characterized by the filling of (n-2)f orbitals.

* **Lanthanoids:** Have general electronic configuration [Xe] 4f$^{n}$ 5d$^{0-1}$ 6s². They are chemically similar and tend to exhibit +3 oxidation state.

* **Actinoids:** Have general electronic configuration [Rn] 5f$^{n}$ 6d$^{0-1}$ 7s². They exhibit a greater variety of oxidation states and are radioactive.

* **Key Compounds:** Potassium Dichromate (K₂Cr₂O₇) and Potassium Permanganate (KMnO₄) are important oxidizing agents.

* **Applications:** Transition metals and their compounds have diverse applications in catalysis, coloring agents, and in the formation of alloys.

Detailed Notes

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1. Transition Elements (D-Block) (00:11)

* Defined by the filling of (n-1)d orbitals.

* Groups 3-12 of the periodic table.

* General electronic configuration: (n-1)d$^{1-10}$ ns$^{1-2}$.

* Have unpaired electrons in d-orbitals, leading to unique properties.

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2. Physical Properties (02:08)

* **Metallic Character:** Generally good metallic character, forming metallic bonds.

* **Melting and Boiling Points:** High melting and boiling points due to strong interatomic metallic bonding, which depends on the number of unpaired d-electrons.

* **Enthalpy of Atomisation (04:00):** Generally high enthalpy of atomisation, indicating strong metallic bonds. This is due to the involvement of both ns and (n-1)d electrons in bonding.

* **Atomic and Ionic Size:**

* Decrease across a period due to increasing nuclear charge pulling valence electrons closer.

* Irregularities exist due to varying shielding effects and electron configurations.

* Ionic radii also decrease across a period for ions of the same charge.

* Size of M$^{2+}$ ions in the first transition series: Sc$^{2+}$ > Ti$^{2+}$ > V$^{2+}$ > Cr$^{2+}$ > Mn$^{2+}$ > Fe$^{2+}$ > Co$^{2+}$ > Ni$^{2+}$ > Cu$^{2+}$ > Zn$^{2+}$. (Note: Cr$^{2+}$ and Cu$^{2+}$ show exceptions due to their electronic configurations).

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3. Ionisation Enthalpy (06:13)

* Increases across a period due to increasing nuclear charge.

* Irregularities are observed due to the complex electron configurations (e.g., stable configurations like d⁵ and d¹⁰ lead to higher ionization enthalpies).

* First ionization enthalpies of 3d series: Sc < Ti < V < Cr > Mn < Fe < Co < Ni > Cu < Zn. (Exceptions at Cr and Cu due to half-filled and fully-filled d-orbitals respectively).

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4. Oxidation State (07:12)

* **Variable Oxidation States:** Transition metals exhibit a wide range of oxidation states due to the small energy difference between ns and (n-1)d electrons. They can lose electrons from both ns and (n-1)d orbitals.

* The highest oxidation state usually corresponds to the total number of valence electrons (ns + (n-1)d).

* The most common oxidation state is +3.

* Example: Manganese (Mn) shows oxidation states from +2 to +7.

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5. Standard Electrode Potential (E°) (10:48)

* **Trend:** The standard electrode potentials (E° for M$^{n+}$/M) across the first transition series are not as simple as expected.

* **Factors influencing E°:**

* Sublimation enthalpy

* Ionization enthalpy

* Hydration enthalpy

* **General Trend:** Generally become more negative across the series, but with significant irregularities.

* **High E° for Cu:** Due to a relatively high enthalpy of hydration and a high ionization enthalpy for Cu(g) → Cu⁺(g) + e⁻, but the stability of the half-filled 3d⁹ configuration in Cu⁺(aq) plays a role.

* **Relatively less negative E° for Zn:** Due to the stability of the fully filled 3d¹⁰ 4s² configuration, making it difficult to remove electrons.

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6. Magnetic Properties (14:24)

* **Paramagnetism:** Most transition metal ions are paramagnetic due to the presence of unpaired electrons in d-orbitals.

* **Ferromagnetism:** Some elements like Fe, Co, Ni exhibit ferromagnetism due to the unpaired electron spins aligning in a domain.

* **Diamagnetism:** Compounds with all paired electrons are diamagnetic.

* **Magnetic Moment (μ):** Calculated using the spin-only formula: μ = √[n(n+2)] BM, where n is the number of unpaired electrons.

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7. Complex Formation (15:40)

* Transition metals readily form complex compounds.

* **Reasons:**

* Small size of the metal ions.

* High positive charge (high charge density).

* Availability of vacant d-orbitals to accept lone pairs of electrons from ligands.

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8. Alloy Formation

* Transition metals form alloys with other metals.

* **Reasons:**

* Similar atomic sizes.

* Similar metallic bonding.

* Comparable electronegativities.

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9. Important Compounds and Applications (18:00 - 24:15)

* **Potassium Dichromate (K₂Cr₂O₇) (18:00):**

* **Structure:** Orange crystalline solid.

* **Preparation:** From iron chromite ore.

* **Oxidizing Agent:** A strong oxidizing agent in acidic medium.

* **Reactions:** Oxidizes Fe²⁺ to Fe³⁺, I⁻ to I₂, SO₃²⁻ to SO₄²⁻.

* **Uses:** In dyeing, electroplating, and as an oxidizing agent.

* **Potassium Permanganate (KMnO₄) (20:39):**

* **Structure:** Purple crystalline solid.

* **Preparation:** From pyrolusite ore (MnO₂).

* **Oxidizing Agent:** A very strong oxidizing agent in acidic, alkaline, and neutral media.

* **Reactions:** Oxidizes Fe²⁺ to Fe³⁺, Mn²⁺ to MnO₂ (in neutral/alkaline), organic impurities.

* **Uses:** In water purification, bleaching, and as a laboratory reagent.

* **Applications of Transition Elements (24:15):**

* **Catalysts:** Many transition metals and their compounds act as catalysts (e.g., Fe in Haber process, Ni in hydrogenation).

* **Coloring Agents:** Due to unpaired d-electrons, their compounds are often colored, used in paints, ceramics, and glass.

* **Alloys:** For making strong and corrosion-resistant materials.

* **Coordination Chemistry:** Formation of complexes.

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10. F-Block Elements (24:50)

* Characterized by the filling of (n-2)f orbitals.

* Also called Inner-transition elements.

* Two series: Lanthanoids and Actinoids.

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#### 10.1 Lanthanoids (25:50)

* Elements from Cerium (Ce, Z=58) to Lutetium (Lu, Z=71).

* General electronic configuration: [Xe] 4f$^{n}$ 5d$^{0-1}$ 6s².

* **Properties:**

* Soft, silvery-white metals.

* Chemically reactive, similar to alkaline earth metals.

* Tarnish in air.

* Melt at low temperatures.

* **Oxidation State of Lanthanoids (28:42):**

* Predominantly +3 oxidation state.

* Some elements show +2 or +4 oxidation states due to the stability of f⁰, f⁷, and f¹⁴ configurations (e.g., Ce⁴⁺, Eu²⁺, Yb²⁺).

* Lanthanoid contraction: Gradual decrease in ionic radii across the series. This is due to the poor shielding effect of f-electrons.

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#### 10.2 Actinoids (29:53)

* Elements from Thorium (Th, Z=90) to Lawrencium (Lr, Z=103).

* General electronic configuration: [Rn] 5f$^{n}$ 6d$^{0-1}$ 7s².

* **Properties:**

* All are radioactive.

* More reactive than Lanthanoids.

* Form many oxidation states, similar to transition metals.

* The last element, Lawrencium (Lr), has the electronic configuration [Rn] 5f¹⁴ 7s².

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#### 10.3 Difference between Actinoids and Lanthanoids (31:26)

| Feature | Lanthanoids | Actinoids |

| :-------------------- | :-------------------------------------------- | :--------------------------------------------- |

| **Orbitals Filled** | (n-2)f orbitals (specifically 4f) | (n-2)f orbitals (specifically 5f) |

| **Electronic Config** | [Xe] 4f$^{n}$ 5d$^{0-1}$ 6s² | [Rn] 5f$^{n}$ 6d$^{0-1}$ 7s² |

| **Radioactivity** | Non-radioactive (except Pm) | All are radioactive |

| **Oxidation States** | Mostly +3; +2, +4 less common | Wide range of oxidation states (+3 to +7) |

| **Chemical Reactivity**| Less reactive, resemble alkaline earth metals | More reactive, resemble transition metals |

| **Complex Formation** | Less tendency to form complexes | Greater tendency to form complexes |

| **Nature of Oxides** | Mostly basic | Amphoteric |

| **Contraction** | Lanthanoid contraction (significant) | Actinoid contraction (less pronounced) |

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