The complete lecture — the d-block comes alive in the live panel as you read. Scroll down; the animation keeps pace, and in the hero scene you can split white light into a single gemstone colour yourself.
1 — Position & defining characteristics
- Transition element — an atom (or common ion) with a partly filled d-subshell; the d-block, Groups 3–12. The 3d series runs Sc → Zn.
Hallmarks: variable oxidation states, coloured ions, paramagnetism, catalysis, complexes and alloys.
2 — Electronic configuration of the 3d series
General(n−1)d¹⁻¹⁰ ns¹⁻² · e.g. Fe = [Ar] 3d⁶ 4s²
Anomalies: Cr = [Ar] 3d⁵ 4s¹ and Cu = [Ar] 3d¹⁰ 4s¹ — a half-filled or full d-set is extra stable, so one 4s electron drops into 3d.
3 — Variable oxidation states
- Why variable? the 3d and 4s electrons are close in energy, so both are available for bonding — different numbers can be lost.
Mn shows +2, +3, +4, +6, +7; Fe shows +2 and +3.
4 — Coloured ions & d-d transitions
d-d transitionligands split the d-orbitals by Δ · electron absorbs hν = Δ · colour seen = complement of light absorbed
Sc³⁺ (3d⁰, empty) and Zn²⁺ (3d¹⁰, full) cannot make a d-d transition, so they are colourless. Move the sliders to change the splitting and watch the transmitted colour shift.
5 — Paramagnetism & unpaired electrons
Spin-only momentμ = √[ n(n+2) ] BM · n = unpaired electrons
Mn²⁺ / Fe³⁺ (3d⁵) → n = 5 → μ ≈ 5.92 BM; Zn²⁺ (3d¹⁰) → n = 0 → diamagnetic.
6 — Catalytic activity
| Process | Catalyst |
|---|
| Haber (NH₃) | Fe |
| Contact (H₂SO₄) | V₂O₅ |
| Hydrogenation | Ni |
Variable oxidation states + surface adsorption give a low-energy path.
7 — Complex (coordination) compounds
- Complex — a central metal ion surrounded by ligands (lone-pair donors). The number of donor atoms is the coordination number (often 4 or 6).
Examples[Cu(NH₃)₄]²⁺ — deep blue, CN 4 · [Fe(CN)₆]⁴⁻ — CN 6
8 — Alloy formation
| Alloy | Metals |
|---|
| Stainless steel | Fe + Cr (+Ni) |
| Brass | Cu + Zn |
| Bronze | Cu + Sn |
9 — Uses of transition elements
- Iron → steel; copper → wiring; chromium → plating.
- Catalysts (Fe, V₂O₅, Ni, Pt); pigments; Fe in haemoglobin, Co in vitamin B₁₂.
10 — Worked questions
config
Cr (Z=24) = [Ar] 3d⁵ 4s¹ — half-filled d⁵ stability.
μ
Mn²⁺ (3d⁵): n=5 → μ = √[5·7] = 5.92 BM.
11 — Exam recap
- d-block position & defining traits.
- 3d configurations; Cr & Cu anomalies; 4s lost first.
- Variable oxidation states; coloured ions & d-d transitions.
- Paramagnetism; μ = √[n(n+2)].
- Catalysis; complexes & coordination number; alloys & uses.