---
title: "VBT for [Ni(NH₃)₆]²⁺: geometry and magnetism"
subject: "Engineering Chemistry"
chapter: 6
key: "semester_2/engineering_chemistry:vbt-nih36"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/vbt-nih36
site: BCT Engineering
---

# VBT for [Ni(NH₃)₆]²⁺: geometry and magnetism

Engineering Chemistry · Chapter 6: Coordination Complexes

- Asked in: 2070 Bhadra, 3 marks; 2068 Bhadra, 3 marks (asked 2 times)
- Video: [Hybridization, Geometry and magnetic properties of Coordination Complexes using VBT](https://www.youtube.com/watch?v=LhfdR9tvo5I) — SK Chemistry 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/vbt-nih36
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-6

## Question

Explain the formation of [Ni(NH₃)₆]²⁺ on the basis of valence bond approach and predict its geometry and magnetic behavior.

## Short answer

[Ni(NH3)6]2+ forms by sp3d2 hybridization using outer 4d orbitals, resulting in an octahedral geometry. It is paramagnetic with two unpaired 3d electrons and a magnetic moment of 2.83 BM.

## Answer

Ni (Z = 28); Ni²⁺ is 3d⁸. NH₃ is a ligand with a lone pair on N, and coordination number is 6.

**Formation:** the 3d electrons of Ni²⁺ stay unpaired (even with pairing, d⁸ can free only one 3d orbital, not the two needed for d²sp³). The six vacant orbitals used are one 4s, three 4p and two 4d, giving sp³d² hybridisation.
```text
Ni²⁺ 3d: [↑↓][↑↓][↑↓][↑ ][↑ ]   4s [ ]  4p [ ][ ][ ]  4d [ ][ ]
                                 \______ sp³d² ______/
                                  six NH₃ lone pairs →
```
- **Geometry:** octahedral (outer orbital complex).
- **Magnetism:** two unpaired 3d electrons, so it is **paramagnetic**, μ = √(2×4) = 2.83 BM.

## Check yourself

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

1. What is the d configuration of Ni2+ (Z = 28)?
   A. 3d8
   B. 3d6
   C. 3d10
   D. 3d9
   Answer: A. Ni (Z=28) minus two electrons. (Key point: Ni2+)

2. [Ni(NH3)6]2+ uses
   A. d2sp3
   B. sp3d2 (one 4s, three 4p, two 4d)
   C. dsp2
   D. sp3
   Answer: B. d8 cannot free two 3d orbitals for d2sp3. (Key point: Hybridisation)

3. What is the geometry of [Ni(NH3)6]2+?
   A. tetrahedral
   B. square planar
   C. octahedral (outer orbital)
   D. linear
   Answer: C. Six NH3 lone pairs. (Key point: Geometry)

4. What is the magnetic behaviour of [Ni(NH3)6]2+?
   A. diamagnetic
   B. paramagnetic with 4 unpaired
   C. paramagnetic with 1.73 BM
   D. paramagnetic with 2 unpaired electrons, 2.83 BM
   Answer: D. mu = sqrt(2x4). (Key point: Magnetism)

## Related in Engineering Chemistry

- [Tetrahedral and square planar complexes; [Ni(NH₃)₄]²⁺ VBT](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atetra-square-vbt-ni-nh3) — Engineering Chemistry, chapter 6
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