---
title: "IUPAC names and EAN of complexes"
subject: "Engineering Chemistry"
chapter: 6
key: "semester_2/engineering_chemistry:iupac-ean"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/iupac-ean
site: BCT Engineering
---

# IUPAC names and EAN of complexes

Engineering Chemistry · Chapter 6: Coordination Complexes

- Asked in: 2073 Bhadra, 4 marks
- Video: [Naming Coordination Compounds - Chemistry](https://www.youtube.com/watch?v=yeNtqjE0dJw) — The Organic Chemistry Tutor
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/iupac-ean
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-6

## Question

Write the IUPAC name of the following complexes compounds and find the Effective Atomic Number of the central metal in these complexes.
(i) [Co(NH₃)₆]Cl₃
(ii) [Cr(H₂O)₄Cl₂]Cl
(iii) [Cu(NH₃)₄]SO₄
(iv) K₃[AlF₆]

## Short answer

IUPAC names: hexaamminecobalt(III) chloride, tetraaquadichlorochromium(III) chloride, tetraamminecopper(II) sulfate, potassium hexafluoroaluminate(III). EAN values: Co 36, Cr 33, Cu 35, Al 22. Only cobalt attains the krypton configuration.

## Answer

EAN = (Z − oxidation state) + 2 × (number of ligand donor pairs).

| Complex | IUPAC name | Metal | Calculation | EAN |
|---|---|---|---|---|
| [Co(NH₃)₆]Cl₃ | hexaamminecobalt(III) chloride | Co³⁺ | 27 − 3 + 12 | 36 |
| [Cr(H₂O)₄Cl₂]Cl | tetraaquadichlorochromium(III) chloride | Cr³⁺ | 24 − 3 + 12 | 33 |
| [Cu(NH₃)₄]SO₄ | tetraamminecopper(II) sulfate | Cu²⁺ | 29 − 2 + 8 | 35 |
| K₃[AlF₆] | potassium hexafluoroaluminate(III) | Al³⁺ | 13 − 3 + 12 | 22 |

**Answer:** EAN of Co = 36, Cr = 33, Cu = 35, Al = 22. Only the cobalt complex reaches the Kr configuration (36).

## Check yourself

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

1. Which formula gives EAN?
   A. (Z - oxidation state) + 2 x number of ligands
   B. Z + oxidation state
   C. Z - 2 x ligands
   D. Z x ligands
   Answer: A. The correct option is: (Z - oxidation state) + 2 x number of ligands. This follows from the answer on ean formula. (Key point: EAN formula)

2. What is the EAN of Co in [Co(NH3)6]Cl3?
   A. 33
   B. 36
   C. 35
   D. 30
   Answer: B. 27 - 3 + 12. (Key point: Co)

3. What is the EAN of Cu in [Cu(NH3)4]SO4?
   A. 36
   B. 33
   C. 35
   D. 31
   Answer: C. The correct option is: 35. This follows from the answer on cu. (Key point: Cu)

4. Which complex has an EAN equal to a noble gas (Kr = 36)?
   A. Cr complex
   B. Cu complex
   C. Al complex
   D. Cobalt complex only
   Answer: D. The correct option is: Cobalt complex only. This follows from the answer on noble gas. (Key point: Noble gas)

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