---
title: "Cu(I) diamagnetic, Cu(II) paramagnetic"
subject: "Engineering Chemistry"
chapter: 5
key: "semester_2/engineering_chemistry:cu1-diamagnetic"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/cu1-diamagnetic
site: BCT Engineering
---

# Cu(I) diamagnetic, Cu(II) paramagnetic

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

- Asked in: 2071 Bhadra, 2.5 marks
- Video: [Cu+1 is diamagnetic while Cu+2 is paramagnetic, explain?](https://www.youtube.com/watch?v=yFzbXyWdb3w) — Learn chemistry with sajjad
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/cu1-diamagnetic
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-5

## Question

Give reason: Cu(I) is diamagnetic whereas Cu(II) is paramagnetic.

## Short answer

Cu(I) has a 3d10 configuration with no unpaired electrons, making it diamagnetic. Cu(II) is 3d9 with one unpaired electron, making it paramagnetic with a magnetic moment of 1.73 BM.

## Answer

Magnetic behaviour depends on unpaired electrons.

- Cu⁺ (Z = 29) has the configuration [Ar] 3d¹⁰. All ten d electrons are paired, so there is no unpaired electron and Cu(I) is **diamagnetic**.
- Cu²⁺ has the configuration [Ar] 3d⁹. One d orbital holds a single electron, so there is one unpaired electron and Cu(II) is **paramagnetic** (μ = √(1×3) = 1.73 BM).

Therefore Cu(I) compounds are diamagnetic and Cu(II) compounds are paramagnetic.

## Check yourself

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

1. What decides whether a species is paramagnetic or diamagnetic?
   A. Total number of electrons
   B. The charge on the ion
   C. The atomic number of the metal
   D. Presence or absence of unpaired electrons
   Answer: D. Unpaired electrons give paramagnetism; all paired gives diamagnetism. (Key point: Basis of magnetism)

2. Why is Cu(I) diamagnetic?
   A. Cu+ is 3d10 with all electrons paired
   B. Cu+ is 3d9 with one unpaired electron
   C. Cu+ is 3d0 with no electrons
   D. Cu+ is 3d8 with two unpaired electrons
   Answer: A. Cu+ has a full d10 subshell, so no unpaired electron. (Key point: Cu+ diamagnetic)

3. What is the configuration of Cu2+ and the number of unpaired electrons?
   A. 3d10, none
   B. 3d9, one unpaired electron
   C. 3d8, two
   D. 3d9, three
   Answer: B. Cu2+ is 3d9 with one unpaired electron, so mu = sqrt(3) = 1.73 BM. (Key point: Cu2+ paramagnetic)

## Related in Engineering Chemistry

- [VBT: magnetism of [Fe(CN)₆]⁴⁻/³⁻ and [Ni(CO)₄]](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Avbt-facts-fecn6-nico4) — Engineering Chemistry, chapter 6
- [IUPAC names and EAN of complexes](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aiupac-ean) — Engineering Chemistry, chapter 6

## Related in other subjects

- [Valid lossless function; Foster II and Cauer II](https://www.bctengineer.com/question.md?key=semester_5%2Ffilter_design%3Alossless-three-functions-foster-cauer-ii) — Filter Design, chapter 4, asked 2×
- [Lossless one-port properties; Foster II and Cauer II](https://www.bctengineer.com/question.md?key=semester_5%2Ffilter_design%3Alossless-one-port-foster-cauer-ii) — Filter Design, chapter 4
- [RC properties; lossless check; Foster series and Cauer II](https://www.bctengineer.com/question.md?key=semester_5%2Ffilter_design%3Arc-properties-lossless-foster-series) — Filter Design, chapter 4
- [Valid RC admittance; Foster II and RC ladder](https://www.bctengineer.com/question.md?key=semester_5%2Ffilter_design%3Arc-admittance-foster-ii-ladder) — Filter Design, chapter 4