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- 2075 Baisakh · 2.5 marks
- 2071 Magh · 2.5 marks
Paramagnetism trend from Sc to Zn
Short answer
For M²⁺ ions, unpaired d electrons increase from 1 (Sc²⁺) to 5 (Mn²⁺), so paramagnetism rises to a maximum. After Mn, added electrons pair up, reducing unpaired electrons to zero at Zn²⁺ (d¹⁰), which is diamagnetic.
Explain why paramagnetic properties increase from Sc to Mn and then decrease to Zn.
Paramagnetism depends on the number of unpaired d electrons.
- From Sc to Mn the number of d electrons in the M²⁺ ions increases from 1 to 5. According to Hund's rule, each added electron occupies a separate d orbital with parallel spin, so the number of unpaired electrons increases from 1 to 5, and paramagnetism increases, reaching a maximum at Mn²⁺ (d⁵).
- After Mn, each new d electron must pair up with one already present, so the number of unpaired electrons decreases from 5 to 0 and paramagnetism falls.
- At Zn (Zn²⁺, d¹⁰) all electrons are paired, so it is diamagnetic.
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) |
For Sc, the common ion Sc³⁺ is d⁰ (diamagnetic), but Sc²⁺ (d¹) and the Sc atom have one unpaired electron.
✓ Answer checked by Claude Opus 5.5 (high effort)
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