---
title: "Paramagnetism trend from Sc to Zn"
subject: "Engineering Chemistry"
chapter: 5
key: "semester_2/engineering_chemistry:paramagnetism-sc-zn"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/paramagnetism-sc-zn
site: BCT Engineering
---

# Paramagnetism trend from Sc to Zn

Engineering Chemistry · Chapter 5: 3-d Transition Elements and their Applications

- Asked in: 2075 Baisakh, 2.5 marks; 2071 Magh, 2.5 marks (asked 2 times)
- Video: [Para magnetic decreases after d5 Why? Part 34|Unit-8 | cbse grade 12 chemistry| d,f block](https://www.youtube.com/watch?v=iDzNzwLI83c) — World of chemistry - class 10, 11 and 12
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/paramagnetism-sc-zn
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-5

## Question

Explain why paramagnetic properties increase from Sc to Mn and then decrease 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.

## Answer

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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Paramagnetism depends on
   A. Number of unpaired d electrons
   B. Atomic mass
   C. Number of neutrons
   D. Ionic charge only
   Answer: A. More unpaired electrons give stronger paramagnetism. (Key point: Trend)

2. From Sc to Mn, why do unpaired electrons increase?
   A. Electrons pair up first
   B. Hund's rule: each new electron enters a separate d orbital with parallel spin
   C. Electrons leave the atom
   D. Electrons enter s orbitals
   Answer: B. Unpaired electrons rise from 1 to 5. (Key point: Hund's rule)

3. Why does paramagnetism decrease after Mn?
   A. Electrons are lost
   B. d orbitals disappear
   C. New electrons pair with existing ones
   D. Neutrons increase
   Answer: C. Unpaired electrons fall from 5 to 0. (Key point: After Mn)

4. Why is Zn2+ diamagnetic?
   A. d5: all unpaired
   B. d0: no electrons, so paramagnetic
   C. d9: one unpaired
   D. d10: all electrons paired
   Answer: D. No unpaired electrons means no net moment. (Key point: Zn)

## Related in Engineering Chemistry

- [Unpaired electrons and paramagnetism; [NiCl₄]²⁻, [Co(NH₃)₆]³⁺](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aparamagnetism-unpaired-ni-co) — Engineering Chemistry, chapter 6

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