---
title: "The Spectrochemical Series, Spin State and Magnetism"
description: "Whether electrons pair up or spread out depends on which costs less, the pairing energy or the jump across the split. Ligands can be ordered by how large a split they cause, and that order predicts ma"
canonical: https://lightmysky.com/learn/science/the-spectrochemical-series-spin-state-and-magnetism-mt_gfKL7W8kg-
source: https://lightmysky.com/learn/science/the-spectrochemical-series-spin-state-and-magnetism-mt_gfKL7W8kg-.md
retrieved: 2026-09-12
---

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# The Spectrochemical Series, Spin State and Magnetism

Whether electrons pair up or spread out depends on which costs less, the pairing energy or the jump across the split. Ligands can be ordered by how large a split they cause, and that order predicts magnetic behaviour.

Subject: Science · Area: Chemistry · Ages 19 to 21
Page: https://lightmysky.com/learn/science/the-spectrochemical-series-spin-state-and-magnetism-mt_gfKL7W8kg-

## Ready when they can

- Compares pairing energy with the splitting energy to assign a high or low spin configuration
- Places common ligands in order of field strength and explains why the order does not follow charge
- Predicts the number of unpaired electrons and converts it to a spin-only magnetic moment
- Explains why tetrahedral complexes are almost always high spin

## Lesson: High spin or low spin

High spin or low spin is a contest of two prices. Promoting an electron across the gap costs the splitting energy, while doubling up inside one orbital costs the pairing energy. If the gap costs more, electrons spread out and stay high spin; if pairing costs less, they double up and go low spin. Whichever bill is smaller wins.

The spectrochemical series ranks ligands by the split they produce, and it is an experimental fact to be used, not derived. Strong field ligands such as cyanide and carbon monoxide sit at the top and force low spin; weak field ligands such as fluoride and water sit at the bottom and allow high spin. Charge does not rule: neutral carbon monoxide outranks negatively charged fluoride, so memorise the order instead of deriving it from charge.

**Example.** A d5 ion shows the stakes. High spin it carries five unpaired electrons, low spin just one, and magnetism tells you which case you hold. Four unpaired electrons give about 4.90 Bohr magnetons, so a measured moment near that value pins the configuration down. Run the logic backwards: count unpaired electrons from the moment, then ask which arrangement gives that count.

**Tip.** Tetrahedral fields are a special case: the gap is so tiny that the pairing price is never worth paying, so tetrahedral complexes are almost always high spin. Octahedral fields allow both outcomes, which is where the series earns its keep.

**Recap.** Compare the gap with the pairing cost, read the ligand's rank in the series, and let the measured moment confirm the spin state.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Crystal Field Theory and the Splitting of d Orbitals](https://lightmysky.com/learn/science/crystal-field-theory-and-the-splitting-of-d-orbitals-mt_YfIBGXj8su)

## Opens up

- [Metals in Biology: Active Sites, Electron Transfer and Chelation](https://lightmysky.com/learn/science/metals-in-biology-active-sites-electron-transfer-and-chelation-mt_gKhjhRXfMU)
- [Ligand Field Theory and Pi Bonding in Complexes](https://lightmysky.com/learn/science/ligand-field-theory-and-pi-bonding-in-complexes-mt_Gq3JG7F7Nl)