d‑ and f‑Block Elements
AP EAMCET – Chemistry
1. Simple Explanation
- d‑block (transition metals) – Elements whose d subshell is being filled.
- f‑block (inner transition metals) – Elements whose f subshell is being filled; divided into
- Lanthanides (4f) – 57 – 71
- Actinides (5f) – 89 – 103
- They sit in the middle of the periodic table (blocks B, D, F).
- Both blocks exhibit a wide range of oxidation states, coloured compounds, and catalytic activity.
2. Key Points
| Feature | d‑Block | f‑Block |
|---|---|---|
| Electronic configuration | ( (n-1)d^{x} ns^{2} ) | ( (n-2)f^{x} (n-1)d^{0–1} ns^{2} ) |
| Common oxidation states | +1, +2, +3, +4, +5, +6 (varies) | +3 (rare), +4, +5, +6 (actinides), often +3 in lanthanides |
| Colour | Many are colourful due to d‑d transitions (e.g., Fe²⁺ – orange) | Lanthanides often sharp‑emission; actinides emit due to f‑f transitions |
| Magnetic behaviour | Paramagnetic (unpaired d electrons) | Paramagnetic (unpaired f electrons) |
| Nuclear magnetic resonance | Poor (paramagnetic broadening) | Poor (paramagnetic) |
| Uses | Catalysts (e.g., Pt, Pd), pigments, magnetic alloys, electronics | Rare‑earth magnets, phosphors, nuclear fuel, catalysts (actinides) |
| Stability | Often high‑valence states are unstable in aqueous media | +3 is most stable for lanthanides; actinides show variable valence |
| Location | Periods 4–7, groups 3–12 | Lanthanide row below period 6; Actinide row below period 7 |
Periodic Trends (d‑Block)
- Atomic radius – decreases across a period, increases down a period (incomplete shielding).
- Ionisation energy – similar trend, but varies due to electronic configuration.
- Metallic character – increases down a group.
Periodic Trends (f‑Block)
- Lanthanide contraction – gradual decrease in ionic radii from La³⁺ to Lu³⁺.
- Actinide contraction – similar but slightly less pronounced.
3. Worked Example
Problem
Determine the electronic configuration of ( \mathrm{Co^{3+}} ) and its number of unpaired electrons.
Solution
-
Ground‑state configuration of Co (Z = 27):
[ \mathrm{Co} : [Ar],4s^{2},3d^{7} ] -
Remove 3 electrons to form ( \mathrm{Co^{3+}} ):
- First, remove the two 4s electrons → (4s^{0}).
- Then remove one 3d electron → (3d^{6}).
[ \mathrm{Co^{3+}} : [Ar],3d^{6} ]
-
Predict electron pairing using Hund’s rule:
- Five 3d orbitals.
- With 6 electrons → one orbital will have a paired set, others single.
Orbital Occupancy Pairing? (d_{xy}) 2 yes (d_{yz}) 1 no (d_{xz}) 1 no (d_{z^2}) 1 no (d_{x^2-y^2}) 1 no -
Number of unpaired electrons: 4.
-
Result:
[ \mathrm{Co^{3+}} : [Ar],3d^{6} \quad \text{(4 unpaired e⁻)} ]
Quick check: In an octahedral complex, ( \mathrm{Co^{3+}} ) is often low‑spin (no unpaired electrons). Our free‑ion calculation gives 4 unpaired electrons; ligand field effects would change this.
4. Quick Revision Summary
| Topic | Points to Remember |
|---|---|
| Where they sit | d‑block: groups 3–12, periods 4–7; f‑block: lanthanides (La‑Lu), actinides (Ac‑Lr) |
| Electronic config | d‑block: ((n-1)d^{x}ns^{2}) |
| Common oxidation states | Transition metals: +1 to +6; Lanthanides: +3; Actinides: +3 to +6 |
| Colour & magnetism | d‑d (transition metals) → colourful, paramagnetic; f‑f (inner) → sharp emission, paramagnetic |
| Uses | Catalysts, pigments, magnetic alloys, rare‑earth magnets, nuclear fuel |
| **Trends |