# Paramagnetic and diamagnetic substances

> Why some substances are pulled into a magnetic field


## Objectives

- Explain how a spinning unpaired electron forms a magnetic field.
- Define paramagnetic and diamagnetic substances in the book's words.
- State that the magnetic moment increases with the number of unpaired electrons.
- Classify a substance from its d configuration and order substances by magnetic moment.

## 1. Magnetic properties and catalytic activity




## 2. Pulled in or pushed out?

Predict: what makes the difference?

- Zinc compounds are not affected by magnets
- Iron is a magnet; zinc is not
- $\ce{Fe^3+}$ has unpaired electrons; in $\ce{Zn^2+}$ all electrons are paired ✓

$\ce{Fe^{3+}}$ ($3d^5$) has unpaired electrons, so $\ce{FeCl3}$ is paramagnetic and is attracted to the magnetic field. In $\ce{Zn^{2+}}$ ($3d^{10}$) all electrons are paired, so $\ce{ZnSO4}$ is diamagnetic and repels the field.

[ar-EG] الـ $\ce{Fe^{3+}}$ ($3d^5$) فيه unpaired electrons، فالـ $\ce{FeCl3}$ بيبقى paramagnetic وبيتجذب للـ magnetic field. أما في الـ $\ce{Zn^{2+}}$ ($3d^{10}$) فالـ electrons كلها paired، فالـ $\ce{ZnSO4}$ بيبقى diamagnetic وبيتنافر مع الـ field.
## 3. A spinning electron

Book p.13: an unpaired electron (↑) forms a magnetic field due to its spinning. Each electron spins. An **unpaired electron** (↑), spinning on its axis, forms a small magnetic field. In a pair (↑↓) the two spins are opposite, so their fields cancel.


## 4. Paramagnetic substances

Unpaired electrons? Then the substance is pulled toward the field. Paramagnetic substance A substance that is attracted to the external magnetic field due to the presence of unpaired electrons. A paramagnetic sample is pulled into the field between two poles. A paramagnetic substance is a magnet.


## 5. Magnetic moment

Magnetic moment The strength of the magnetism of a substance's atoms or ions. It increases with the number of unpaired electrons. Add d electrons one at a time, by Hund's rule. Watch the unpaired electrons. electrons in the d sublevel d⁰ d¹ d² d³ d⁴ d⁵ d⁶ d⁷ d⁸ d⁹ d¹⁰ $d^5$: one electron in each box. 5 unpaired: the largest magnetic moment a d sublevel can give. $d^{10}$: the most d electrons, yet none unpaired. Magnetic moment zero. More electrons make a substance more magnetic.


## 6. Diamagnetic substances

All electrons paired? Then every field cancels. Diamagnetic substance A substance that repels the external magnetic field, due to the pairing of all its electrons. Its magnetic moment equals zero. A diamagnetic sample is pushed out of the field. A diamagnetic substance is not affected by a magnetic field.


## 7. The book's exercise

Book exercise, p.14: which is paramagnetic, which is diamagnetic? Then order their magnetic moments. Zn ($d^{10}$) $\ce{Ni^2+}$ ($d^8$) Iron(II) chloride, $\ce{Fe^2+}$ ($d^6$) Book's answer, p.14 Order of magnetic moment: Zn < $\ce{Ni^2+}$ < iron(II) chloride.


## 8. Which pulls hardest?

Which ion has the largest magnetic moment?

- $\ce{Cr^3+}$ ($3d^3$)
- $\ce{Co^2+}$ ($3d^7$)
- $\ce{Cu+}$ ($3d^{10}$)
- $\ce{Fe^3+}$ ($3d^5$) ✓

Unpaired: $3d^{10}$ 0, $3d^3$ 3, $3d^7$ 3, $3d^5$ 5. The magnetic moment follows the unpaired electrons, not the total.

[ar-EG] عدد الـ unpaired: الـ $3d^{10}$ فيه 0، والـ $3d^3$ فيه 3، والـ $3d^7$ فيه 3، والـ $3d^5$ فيه 5. الـ magnetic moment ماشي ورا عدد الـ unpaired electrons، مش العدد الكلي.
## 9. Sort the ions

Sort these ions. Picture their 3d boxes first. A diamagnetic substance ___ the external magnetic field, because all its electrons are ___.


## 10. Summary

A spinning unpaired electron forms a magnetic field; paired spins cancel. **Paramagnetic**: attracted to the external field (unpaired electrons). Most compounds of the transition elements are paramagnetic. **Diamagnetic**: all electrons paired, magnetic moment zero, repels the external field. Magnetic moment increases with the number of unpaired electrons. Give reasons: most transition elements are attracted to the external magnetic field Because they have **unpaired electrons** in the d sublevel. Spinning unpaired electrons form a **magnetic field**, so the substance is **paramagnetic**. Back to the hook: $\ce{Fe^3+}$ ($3d^5$) has unpaired electrons; $\ce{Zn^2+}$ ($3d^{10}$) has none. Can you explain why $d^{10}$ gives zero magnetic moment? In $d^{10}$ all five boxes hold a pair (↑↓). In a pair the two spins are opposite, so their fields cancel: no unpaired electrons, magnetic moment zero. $d^{10}$: 0 unpaired



Chapter: Transition Elements (https://yaani.ai/en/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/en/lesson/chem-s3-en.lesson-te.magnetic-properties