JEE Chemistry D-Block Elements Complete Guide

D-block elements, also known as transition metals, occupy groups 3 to 12 in the periodic table. They are characterized by the filling of d-orbitals and show unique properties that are crucial for JEE Mains and Advanced chemistry exams. This guide covers their electronic configurations, general properties, oxidation states, important compounds, and coordination chemistry, enabling you to master this vital topic.

1. Electronic Configuration of D-Block Elements

The general electronic configuration of d-block elements is:

(n-1)d^{1-10} ns^{0-2}

For example,

• Scandium (Sc): \( [\mathrm{Ar}]\, 3d^1\, 4s^2 \)
• Iron (Fe): \( [\mathrm{Ar}]\, 3d^6\, 4s^2 \)
• Copper (Cu): \( [\mathrm{Ar}]\, 3d^{10}\, 4s^1 \)

Note that exceptions occur to achieve more stable half-filled or completely filled d-subshells, e.g., Chromium (Cr) and Copper (Cu).

2. General Characteristics of D-Block Elements

• Variable Oxidation States: Commonly exhibit multiple oxidation states due to involvement of both ns and (n-1)d electrons.
• Formation of Colored Compounds: Partially filled d-orbitals allow d-d transitions, causing characteristic colors.
• Magnetic Properties: Due to unpaired d-electrons, many d-block elements and their compounds show paramagnetism.
• High Melting and Boiling Points: Strong metallic bonding because of d-electrons.
• Catalytic Activity: Many act as catalysts in industrial processes.
• Formation of Complexes: Ability to form coordination compounds due to vacant d-orbitals.

3. Oxidation States

D-block elements show a variety of oxidation states. The maximum oxidation state equals the group number.

3.1 Stability of Oxidation States

Stability depends on electronic configuration and extra stability for half-filled and fully-filled d-orbitals. Example:

• Chromium: \( \mathrm{Cr}^{3+} (3d^3) \) is more stable than \( \mathrm{Cr}^{2+} (3d^4) \) due to half-filled configuration.
• Copper: \( \mathrm{Cu}^{+} (3d^{10}) \) is more stable than \( \mathrm{Cu}^{2+} (3d^9) \).

4. Important D-Block Element Groups

4.1 Group 3 to 5: Scandium, Titanium, Vanadium

• Titanium: Known for its oxide \( \mathrm{TiO}_2 \), used as white pigment and catalyst.
• Vanadium: Exhibits oxidation states +2 to +5; \( \mathrm{V}_2\mathrm{O}_5 \) used in contact process for sulphuric acid.
• Uses: Alloys, pigments, catalysts, and steel hardening.

4.2 Group 6: Chromium, Molybdenum, Tungsten

• Chromium: Famous for corrosion resistance (stainless steel) and oxidation states +2 to +6.
• Molybdenum: Catalyst in petroleum industry.
• Tungsten: Very high melting point, used in filaments.

4.3 Group 7: Manganese

• Exhibits oxidation states +2 to +7.
• Used in batteries (\( \mathrm{MnO}_2 \)), steel alloying, and pigments.
• \( \mathrm{KMnO}_4 \) is a strong oxidizing agent used in redox reactions.

4.4 Group 8-10: Iron, Cobalt, Nickel

• Iron: Vital for biological systems (hemoglobin) and industry (steel).
• Cobalt: Important for magnets and vitamin B12.
• Nickel: Used in alloys, batteries, and catalysts.

4.5 Group 11: Copper, Silver, Gold

• Known as coinage metals, with high conductivity and corrosion resistance.
• Used extensively in electrical wiring, jewelry, and coins.

4.6 Group 12: Zinc, Cadmium, Mercury

• Show d\(^{10}\) configuration, often not considered typical transition metals.
• Zinc: Used in galvanization.
• Cadmium: Toxic, used in batteries.
• Mercury: Liquid metal at room temperature, used in thermometers.

5. Complex Formation and Coordination Chemistry

D-block elements form complexes with ligands (molecules/ions with lone pairs).

5.1 Coordination Number and Geometry

• Coordination Number (CN): Number of ligand donor atoms attached to central atom.
• Common CNs: 4 (tetrahedral, square planar), 6 (octahedral).

5.2 Ligands

• Monodentate: Ligands binding through one donor atom, e.g., \( \mathrm{NH}_3 \), \( \mathrm{Cl}^- \).
• Bidentate: Ligands binding through two donor atoms, e.g., ethylenediamine.
• Polydentate (Chelates): Ligands binding through multiple sites.

5.3 Nomenclature of Complexes

Order of naming ligands alphabetically followed by metal and oxidation state in roman numerals.

Example: \([ \mathrm{Cu}( \mathrm{NH}_3 )_4 ] \mathrm{SO}_4 \) - Tetraammine copper(II) sulfate.

5.4 Isomerism in Complexes

• Geometrical isomerism: Cis-trans forms.
• Optical isomerism: Mirror image forms.
• Linkage isomerism: Different atoms of ligand bind.

5.5 Crystal Field Theory (CFT)

Explains color, magnetic properties, and stability of complexes based on splitting of d-orbitals in ligand field.

For octahedral complexes, d-orbitals split into:

t_{2g} (d_{xy}, d_{xz}, d_{yz}) \text{ lower energy} < e_g (d_{z^2}, d_{x^2-y^2}) \text{ higher energy}

Splitting energy is called crystal field splitting energy \( \Delta_0 \).

5.6 High Spin and Low Spin Complexes

Depending on ligand field strength, electrons either fill higher orbitals or pair in lower orbitals:

• High Spin: Weak field ligands, more unpaired electrons.
• Low Spin: Strong field ligands, fewer unpaired electrons.

6. Important Reactions of D-Block Elements

6.1 Reaction with Acids and Bases

• Metallic d-block elements react with acids to produce \( \mathrm{H}_2 \) gas.
• Amphoteric oxides react with both acids and bases.

6.2 Oxidation and Reduction

• Oxidation states vary, redox reactions are common.
• Example: \( \mathrm{Fe}^{2+} \) can be oxidized to \( \mathrm{Fe}^{3+} \).

6.3 Formation of Metal Carbonyls

D-block elements form metal carbonyls such as \( \mathrm{Fe}(\mathrm{CO})_5 \), \( \mathrm{Ni}(\mathrm{CO})_4 \). These are important in organometallic chemistry.

6.4 Reaction with Ligands

Ligand substitution and addition reactions form various coordination compounds.

7. Important Notes for JEE

• Memorize electronic configurations especially exceptions.
• Understand oxidation state trends and stability reasons.
• Practice naming and writing coordination compounds.
• Grasp basics of Crystal Field Theory and related magnetic/optical properties.
• Revise common industrial uses and important reactions.

8. Summary Table of D-Block Elements

Mastering the D-block elements will give you an edge in JEE Chemistry, especially in questions related to coordination compounds, redox chemistry, and industrial applications. Regular practice and understanding underlying concepts are key to excelling.