Transition Elements: MDCAT Notes and MCQs
d-block / transition elements
- Elements whose atoms or ions have partially filled d-orbitals. Groups 3–12; general configuration (n−1)d1–10 ns1–2.
- Zn, Cd, Hg (d10 in atom and ions) are d-block but not typical transition elements. Sc (forms only Sc3+, d0) is also non-typical.
First transition series (3d)
| Element | Configuration |
|---|---|
| Sc (21) | [Ar] 3d1 4s2 |
| Ti (22) | [Ar] 3d2 4s2 |
| V (23) | [Ar] 3d3 4s2 |
| Cr (24) | [Ar] 3d5 4s1 |
| Mn (25) | [Ar] 3d5 4s2 |
| Fe (26) | [Ar] 3d6 4s2 |
| Co (27) | [Ar] 3d7 4s2 |
| Ni (28) | [Ar] 3d8 4s2 |
| Cu (29) | [Ar] 3d10 4s1 |
| Zn (30) | [Ar] 3d10 4s2 |
Ions
When transition metals form ions, 4s electrons are removed first, then 3d. Fe2+ = [Ar] 3d6; Fe3+ = [Ar] 3d5 (more stable, half-filled); Cu+ = [Ar] 3d10; Cu2+ = [Ar] 3d9; Mn2+ = [Ar] 3d5; Zn2+ = [Ar] 3d10.
Characteristic properties
- Variable oxidation states (Mn: +2 to +7) — 4s and 3d energies are close.
- Coloured ions due to d–d transitions (Cu2+ blue; d0 and d10 ions like Sc3+, Zn2+, Cu+ are colourless).
- Paramagnetism from unpaired electrons (magnetic moment μ = √[n(n+2)] BM; Mn2+/Fe3+ with 5 unpaired electrons are strongly paramagnetic).
- Form complexes, act as catalysts (Fe in Haber, Ni in hydrogenation, V2O5 in contact process), form alloys, high m.p. and density.
PMDC learning outcomes for this unit
- Electronic Structure: 12.1 Describe the electronic structures of the elements and ions of d-block elements.