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ELECTRON PAIRING

After completing this section you will be able to do the following:

  • Explain what paired and unpaired electrons are.
  • Explain how paired electrons affect the magnetic properties of a material.

Questions

  1. What are paired electrons?
  2. How do paired electrons affect the magnetic properties of a material?

Since all matter is made up of atoms and all atoms have electrons that are in motion, do all atoms have magnetic fields?

The answer to this question is yes and no. All the electrons do produce a magnetic field as they spin and orbit the nucleus; however, in some atoms, two electrons spinning and orbiting in opposite directions pair up and the net magnetic moment of the atom is zero. Remember that the direction of spin and orbit of the electron determines the direction of the magnetic field. Electron pairing occurs commonly in the atoms of most materials. In the experiment you observed a helium atom showing two electrons spinning and orbiting around the protons and neutrons of the nucleus. The two electrons are paired, meaning that they spin and orbit in opposite directions. Since the magnetic fields produced by the motion of the electrons are in opposite directions, they add up to zero. The overall magnetic field strength of atoms with all paired electrons is zero.

In general, materials that have all paired electrons in the atoms and thus have no net magnetic moment are called diamagnetic materials; yet, there are some exceptions. When placed in the magnetic field of a magnet, diamagnetic materials will produce a slight magnetic field that opposes the main magnetic field. Both ends of a bar magnet will repel a diamagnetic material. If a diamagnetic material is placed in a strong external magnetic field, the magnetic field strength inside the material will be less than the magnetic field strength in the air surrounding the material. The slight decrease in the field strength is the result of realignment in the orbit motion of the electrons. Diamagnetic materials include zinc, gold, mercury, and bismuth.

Another key concept in magnetism is that diamagnetic materials will oppose an applied magnetic field. Both ends of a magnet will repel diamagnetic materials.

Are all materials that have unpaired electrons magnetic?

Most materials with one or more unpaired electrons are at least slightly magnetic. Materials with a small attraction to a magnet are called paramagnetic materials, and those with a strong attraction are called ferromagnetic materials. Aluminum, platinum, and manganese are some paramagnetic materials. Iron, cobalt, and nickel are examples of ferromagnetic materials.