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ChemWiki: The Dynamic Chemistry E-textbook > Inorganic Chemistry > Descriptive Chemistry > Periodic Table of the Elements > Magnetic Properties

Magnetic Properties

The magnetic moment of a system measures the strength and the direction of its magnetism. The term itself usually refers to the magnetic dipole moment. Anything that is magnetic, like a bar magnet, or a loop of electric current can have their own magnetic moments. A magnetic moment is a quantity that has magnitude and direction.  Electrons have an electron magnetic dipole moment. A dipole is symmetric about the direction of its moment. This magnetic moment of an electron is generated by the electron’s intrinsic property of spinning, or an electric charge in motion. There are many different magnetic properties: Paramagnetic, Diamagnetic, Ferromagnetic, Ferromagnetic, etc...

What is Paramagnetism?

The paramagnetic property refers to an atom with one or more unpaired electrons. The unpaired electrons attract a magnetic field due to the electron's magnetic dipole moment. The magnetic dipole moment is defined as the electron's capability to spin. Hund's Rule states that electrons must occupy every orbital in a single manner. This may leave the atom with many unpaired electrons. Being the only electron that can spin in either direction, it can also attain its magnetic moment in any direction. As a result, since Paramagnetic substances have an unpaired electron, the electron is free to align its magnetic moment in any direction. Therefore paramagnetic atoms are capable of being attracted to magnetic fields. Oxygen provides for a good example of being paramagnetic.  We can observe how oxygen is attracted into a magnetic field in the following video. As shown in the video, oxygen is attracted into a magnetic field between two metal balls.

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In the video above it shows an experiment done with liquid oxygen and liquid nitrogen. Oxygen is paramagnetic so it is attracted to the magnetic. Nitrogen is diamagnetic so doesn’t get attracted to magnetic.

There are some exeptions to paramagnetism being located in the transiton metals since some do not have an unpaired electron in the d-orbital. Examples of these metals includeSc3+, Ti4+, Zn2+and Cu+. Since these metals are the not defined as paramagnetic, they are diamagnetic since it has paired electrons. 

Paramagnetic properties also have the capabilities to transition into a solid state due to the clustering of the metal atoms. This is otherwise known as ferromagnetism, but we will not go into depth with this yet, since it is beyond our context.

What is a Diamagnetism?

In contrary, diamagnetic substances have paired electrons. According to the Pauli Exclusion Principle which states that no two identical electrons may take up the same quantum state at the same time, the electron spin must be pointing in opposite directions. This causes the magnetic fields of the electrons to cancel out, thus they do not have any net magnetic field and are not attracted into magnetic field. This leads to diamagnetic substances being weakly repelled by the magnetic field. In short, diamagnetic substances do not have any unpaired electrons, so they do not have any net magnetic moment, therefore they are not attracted into the magnetic field. In the video below, we can observe how water has a diamagnetic property. In the video, water repels magnet. When a magnet is moved under bowl of water, we can see the change in reflection.

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How to determine if a substance is paramagnetic or diamagnetic?

We can tell if a substance is paramagnetic or diamagnetic by looking at its electron configuration and whether it has unpaired electrons or not. If a substance does have unpaired electrons, then it is paramagnetic. If not, then it is diamagnetic. Usually we can break it down to four easy steps.

  1. Get the electron configuration
  2. Draw the electron orbitals
  3. See if there is any unpaired electron(s)
  4. Determine whether the substance is paramagnetic or diamagnetic
 
Example 1: Chlorine atoms

Step 1: Get the electron configuration

For Cl, the electron configuration is 3s23p5

Step 2: Draw the electron orbitals

Cl.jpg

Step 3: See if there is any unpaired electron(s)

There is one unpaired electron.

Step 4: Determine whether the substance is paramagnetic or diamagnetic

Since there is an unpaired electron, Cl atoms are paramagnetic.

Example 2: Zinc Atoms

Step 1: Get the electron configuration.

For Zn, the electron configuration is 4s23d10

Step 2: Draw the electron orbitals.

Zn.jpg

Step 3: See if there is any unpaired electron(s).

There are no unpaired electrons.

Step 4: Determine whether the substance is paramagnetic or diamagnetic.

Since there is no unpaired electron, Zn atoms are diamagnetic

Problems

  1. How many unpaired electrons are found in Oxygen atoms ? 
  2. How many unpaired electrons are found in Bromine atoms? 
  3. Indicate whether Boron atoms are paramagnetic or diamagnetic. 
  4. Indicate whether F- ions are paramagnetic or diamagnetic. 
  5. Indicate whether Fe2+ ions are paramagnetic or diamagnetic.

Answers

1. O has 2s22p4 as electron configuration.

 

O.jpg

Therefore, O has 2 unpaired electrons.

2. Br has 4s23d104p5 has electron configuration. 

 

Br.jpg

Therefore, Br has 1 unpaired electron.

3. B has 2s22p1 as electron configuration.

 

 b.jpg

Because it has one unpaired electron, it is paramagnetic.

4. F- has 2s22p6 has electron configuration.

 

 F.jpg

Because it has no unpaired electron, it is diamagnetic.

 

5. Fe2+ has 3d6 has electron configuration.

 

 Fe.jpg

Because it has 4 unpaired electrons, it is paramagnetic. 

References

  1. Pettrucci, Ralph H. General Chemistry: Principles and Modern Applications. 9th. Upper Saddle River: Pearson Prentice Hall, 2007
  2. Sherman, Alan, Sharon J. Sherman, and Leonard Russikoff. Basic Concepts of Chemistry Fifth Edition. Boston, MA: Houghton Mifflin Company, 1992. Print.
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Last Modified
11:19, 10 Jan 2014

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