---
title: "Transition elements; configuration; paramagnetism"
subject: "Engineering Chemistry"
chapter: 5
key: "semester_2/engineering_chemistry:tm-config-paramagnetism"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/tm-config-paramagnetism
site: BCT Engineering
---

# Transition elements; configuration; paramagnetism

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

- Asked in: 2073 Bhadra, 1+2+2 marks
- Video: [13.1  Transition Metals, their Complexes and Magnetism [HL IB Chemistry]](https://www.youtube.com/watch?v=OC00k_iY36s) — Richard Thornley
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/tm-config-paramagnetism
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-5

## Question

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.

## 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.

## Answer

#### 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) |

## Check yourself

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

1. Transition elements are
   A. All s-block elements
   B. d-block elements with incomplete d in atom or common ion, except Zn, Cd, Hg
   C. All d-block elements
   D. Only noble gases
   Answer: B. Zn, Cd, Hg have d10. (Key point: Definition)

2. Why does Cr have 3d5 4s1?
   A. It has fewer electrons
   B. Half-filled d5 has extra stability
   C. 4s is always empty
   D. It is a noble gas
   Answer: B. Exchange energy and symmetry stabilise d5 and d10. (Key point: Cr and Cu exception)

3. Cu has configuration
   A. [Ar] 3d9 4s2
   B. [Ar] 3d8 4s2
   C. [Ar] 3d10 4s1
   D. [Ar] 3d11
   Answer: C. Full d10 gives stability. (Key point: Cu config)

4. Paramagnetism arises from
   A. Paired electrons
   B. Protons
   C. Unpaired electrons
   D. Complete shells
   Answer: C. Their spin moments align with the field. (Key point: Paramagnetism cause)

## Related in Engineering Chemistry

- [Characteristics of transition series; first-row configuration](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atm-characteristics-config) — Engineering Chemistry, chapter 5
- [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
- [General outer electronic configuration of transition elements](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atm-general-config) — Engineering Chemistry, chapter 5
- [Transition elements; first series configuration](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awhy-transition-elements-typical) — Engineering Chemistry, chapter 5
- [Transition elements; why so called; 3d configurations](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atm-called-config) — Engineering Chemistry, chapter 5
- [First-row configuration; variable oxidation states](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aconfig-variable-oxidation) — Engineering Chemistry, chapter 5

## Related in other subjects

- [Elements of transition curve](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Atransition-curve-elements) — Surveying II, chapter 6