🟣 This is Higher Level (HL) content.
Transition metals (d-block, excluding Sc and Zn) have significantly higher melting points than s-block metals. This is due to the participation of d-electrons in the delocalised electron sea.
📘 IB Definition – Transition Element
A transition element is a d-block element that forms at least one stable ion with a partially filled d-sublevel.
Why Zn and Sc are excluded: Zn only forms Zn²+ (3d¹&sup0; – full d-sublevel). Sc only forms Sc³+ (3d&sup0; – empty d-sublevel). Neither has a partially filled d-sublevel in any stable ion.
Why Transition Metals Bond More Strongly
- Transition metals can delocalise both their s- and d-electrons into the electron sea
- More delocalised electrons → greater electron density in the sea
- Higher cation charge + more electrons → stronger electrostatic attraction
- Transition metal cations are also smaller (greater effective nuclear charge) → electrons are held more tightly
Comparison: s-Block vs d-Block
| Na (s-block) | Fe (d-block) | |
|---|---|---|
| Delocalised electrons | 1 per atom (3s¹) | Multiple (4s + 3d electrons) |
| Cation charge | +1 | +2 or +3 |
| Ionic radius | Larger (102 pm) | Smaller (77 pm for Fe²⁺) |
| Melting point | 98 °C | 1538 °C |
⚠️ Examiner Trap
Do not say d-block metals have "more metallic bonds." The correct explanation is: more electrons are delocalised and the cation charge is higher, resulting in a stronger electrostatic attraction between the cations and the electron sea.
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