d‑Block & f‑Block Elements
Program: COMEDK | Subject: Chemistry
Why study this?
d‑ and f‑block elements are the “medals” of the periodic table – they give us metals with high melting points, varied oxidation states, magnetic & coloured compounds, and many technological applications (electronics, catalysts, nuclear energy, etc.). Understanding their trends is essential for solving quantitative & qualitative questions in the COMEDK exam.
1. Simple Explanation
| Block | Placement | Electron Config. | Key Characteristics |
|---|---|---|---|
| d‑block (Transition Metals) | Groups 3–12, Periods 4–6 (3d, 4d, 5d) | Partially filled d‑orbitals: ns² (n–1)dⁿ |
Variable oxidation states, coloured, often paramagnetic, high melting/boiling points |
| f‑block (Lanthanides & Actinides) | Two separate rows below the main table (4f & 5f) | Partially filled f‑orbitals: ns² (n–1)d¹ (n–2)fⁿ |
Mostly 3+ oxidation state (lanthanides), more radioactive & heavier (actinides); magnetic & luminescent in many compounds |
- d‑block: “Transition” because they can transition between oxidation states easily.
- f‑block: “Inner transition metals” with inner f‑orbitals shielding the outer electrons.
2. Key Points (Exam‑Focused)
| Aspect | d‑block | f‑block |
|---|---|---|
| Periodic Trends | <ul><li>Atomic radius decreases left → right (effective nuclear charge ↑)</li><li>Ionisation energy rises left → right, then drops at Fe (half‑filled d¹⁰)</li><li>Electronegativity slightly ↑ across period</li></ul> | <ul><li>Lanthanide contraction: small size increase across 4f series</li><li>Ionisation energy slowly rises; 5f series shows larger variation (actinides)</li><li>Electronegativity relatively low but increases across a series</li></ul> |
| Oxidation States | Multiple (e.g., Fe: 0, +2, +3; Cu: +1, +2; Zn: +2 only) | Mainly +3 (lanthanides), +4, +3, +2, +1 (actinides) |
| Magnetism | Many are paramagnetic (unpaired d‑electrons) | Lanthanides: 4f electrons give strong paramagnetism; actinides also paramagnetic |
| Colour | Most form coloured complexes (d–d transitions) | Many f‑elements give intense colours due to f–f transitions |
| Hardness & Melting Point | High melting points (most > 1000 °C) | Lanthanides: softer than d‑block; actinides: vary, often high melting |
| Applications | Catalysts (e.g., Pt, Pd), electronics (Cu, Zn), magnetic materials (Fe, Co) | MRI contrast agents (Gd), nuclear fuel (U, Pu), phosphors (Eu) |
| Shielding | d‑orbitals shield less effectively → more chemical reactivity | f‑orbitals shield better → elements behave similarly (lanthanide contraction) |
3. Electron Counting & Shell Filling
- d‑block:
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