Chapter 4 · Chemistry
Zinc Is in the d-Block, So Why Is It Not a Transition Metal?
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A transition element has an incompletely filled d subshell in its atom or in a common ion. Iron (3d⁶) passes; copper (3d¹⁰ atom) passes through Cu²⁺ (3d⁹); zinc stays 3d¹⁰ even as Zn²⁺, so Zn, Cd and Hg are d-block but not transition metals.
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d-Block Configurations: Why Chromium and Copper Break the RuleThe d-block's general configuration is (n−1)d¹⁻¹⁰ ns¹⁻², with 4s filling before 3d. Chromium (3d⁵4s¹) and copper (3d¹⁰4s¹) move one 4s electron into 3d, because 3d and 4s are very close in energy and half-filled and full d sets are extra stable.Chemistry
Key points
- A transition element has an incompletely filled d subshell in its atom or in any common ion.
- Fe: 3d⁶ 4s², incomplete → transition metal.
- Cu: 3d¹⁰ 4s¹ in the atom, but Cu²⁺ is 3d⁹ → transition metal.
- Zn, Cd, Hg: d¹⁰ in the atom and in their ions → d-block, but not transition metals.
The test, case by case
| Element | Atom | Common ion | Transition metal? |
|---|---|---|---|
| Iron, Fe | [Ar] 3d⁶ 4s² | Fe²⁺ 3d⁶, Fe³⁺ 3d⁵ | Yes (incomplete d) |
| Copper, Cu | [Ar] 3d¹⁰ 4s¹ | Cu²⁺ 3d⁹ | Yes (through the ion) |
| Zinc, Zn | [Ar] 3d¹⁰ 4s² | Zn²⁺ 3d¹⁰ | No (always full) |
When a d-block atom forms an ion, the 4s electrons leave first, then 3d electrons.
Group 12
Zinc, cadmium and mercury keep a full (n−1)d¹⁰ subshell in the atom and in their common ions, so they are not regarded as transition metals, though they belong to the d-block.
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