Class 12 Chapter 2 Introduction to transition elements d and f block elements
Introduction
Transition elements, comprising the d‑block and f‑block of the periodic table, exhibit unique electronic structures and versatile chemistry. They play vital roles in catalysis, materials science, and biological systems.
Definition & Position in Periodic Table
d‑Block (Transition Metals): Elements in groups 3–12 whose atoms have an incomplete d‑subshell or can form cations with an incomplete d‑subshell.
f‑Block (Inner Transition Elements): Lanthanides and actinides filling their 4f and 5f orbitals, located below the main table.
| Block | Period | Groups/Series |
|---|---|---|
| d‑Block | 4–7 | Groups 3–12 (Sc→Zn, Yb→Hg) |
| f‑Block | 6–7 | Lanthanides (La–Lu), Actinides (Ac–Lr) |
General Electronic Configurations
- d‑Block: (n–1)d¹⁻¹⁰ ns⁰⁻²
- Lanthanides: [Xe] 4f¹⁻¹⁴ 5d⁰⁻¹ 6s²
- Actinides: [Rn] 5f¹⁻¹⁴ 6d⁰⁻¹ 7s²
Properties of d‑Block Elements
- Variable oxidation states
- Colored ions and compounds
- Magnetic behavior (paramagnetism due to unpaired electrons)
- Catalytic activity (e.g., Fe in Haber process, V₂O₅ in contact process)
- Formation of complex ions
Properties of f‑Block Elements
- Lanthanide contraction (gradual decrease in ionic radii)
- Mostly +3 oxidation state (actinides show +2 to +6)
- Paramagnetic due to unpaired f‑electrons
- High coordination numbers and complex formation
- Radioactivity in many actinides
Comparison: d‑Block vs f‑Block
| Feature | d‑Block | f‑Block |
|---|---|---|
| Oxidation States | Multiple, wide range | Lanth: +3; Actinides: +2 to +6 |
| Color | Often colored | Typically pale or white; some colored |
| Catalysis | Widely used | Limited |
| Magnetism | Paramagnetic | Strongly paramagnetic |
| Applications | Industrial catalysts, alloys | Magnets, nuclear fuel |
Important Applications
- d‑Block: Steel (Fe–C alloys), catalytic converters (Pt, Pd), electroplating (Cr, Ni)
- f‑Block: Permanent magnets (Nd₂Fe₁₄B), phosphors (Eu³⁺ in TV screens), nuclear reactors (U, Pu)
Conclusion
d‑ and f‑block elements enrich chemistry with their diverse oxidation states, coordination chemistry, and technological applications. Mastery of their properties underpins advanced studies in inorganic and materials chemistry.
