- 2073 Bhadra · 1+2+2 marks
Transition elements; configuration; paramagnetism
Short answer
Transition elements have an incomplete d subshell in the atom or common ion. First row configurations: Sc [Ar]3d1 4s2 to Zn [Ar]3d10 4s2, with Cr 3d5 4s1 and Cu 3d10 4s1. Paramagnetism arises from unpaired electrons; each unpaired electron has a spin magnetic moment that aligns with a magnetic field, and more unpaired electrons give stronger paramagnetism.
What are transition elements? Write the electronic configurations of the 1st row transition series. The paramagnetism of substance is due to the presence of unpaired electrons. Explain.
Transition elements
Elements with an incompletely filled d subshell in the atom or in a common ion (the d-block elements, except Zn, Cd and Hg).
Electronic configuration of the first row (3d series)
| Element | Z | Configuration |
|---|---|---|
| Sc | 21 | [Ar] 3d¹ 4s² |
| Ti | 22 | [Ar] 3d² 4s² |
| V | 23 | [Ar] 3d³ 4s² |
| Cr | 24 | [Ar] 3d⁵ 4s¹ (exception) |
| 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 (exception) |
| Zn | 30 | [Ar] 3d¹⁰ 4s² |
The exceptions Cr and Cu arise because half-filled (d⁵) and fully filled (d¹⁰) subshells have extra stability (exchange energy and symmetry). General formula: (n−1)d¹⁻¹⁰ ns¹⁻².
Paramagnetism and unpaired electrons
Paramagnetism is the property of being weakly attracted by a magnetic field. It is due to the presence of unpaired electrons: each unpaired electron has a net spin magnetic moment (and orbital contribution) that aligns with the applied field. Substances with all electrons paired are diamagnetic (repelled weakly).
Transition metal ions have partly filled d orbitals, so most have unpaired electrons and are paramagnetic. The more unpaired electrons, the greater the paramagnetism (spin-only value shown below).
Spin-only magnetic moment: μ = √(n(n+2)) BM, where n = number of unpaired electrons.
| Ion (d-configuration) | Unpaired e⁻ (n) | μ (BM) |
|---|---|---|
| Sc²⁺/Ti³⁺ (d¹) | 1 | 1.73 |
| Ti²⁺ (d²) | 2 | 2.83 |
| V²⁺ (d³) | 3 | 3.87 |
| Cr²⁺ (d⁴) | 4 | 4.90 |
| Mn²⁺ (d⁵) | 5 | 5.92 |
| Fe²⁺ (d⁶) | 4 | 4.90 |
| Co²⁺ (d⁷) | 3 | 3.87 |
| Ni²⁺ (d⁸) | 2 | 2.83 |
| Cu²⁺ (d⁹) | 1 | 1.73 |
| Zn²⁺ (d¹⁰) | 0 | 0 (diamagnetic) |
✓ Answer checked by Claude Opus 5.5 (high effort)
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