Amy has taught university-level earth science courses and has a PhD in Geology.
One of the ways in which you can create levitation is through diamagnetism. In this image, you see a man-made material called pyrolytic carbon floating over magnets.
The reason this material levitates is because it is diamagnetic, which means that the material is repelled by an external magnetic force. This is the opposite of paramagnetism, where objects are attracted to external magnetic fields, much like the attraction between a magnet and a refrigerator.
In this lesson, we're going to examine why some substances are diamagnetic and some are paramagnetic. We'll learn more about the definition of these terms, and discover what they tell you about the properties of the substances.
To understand magnetism in atoms, we must review electron configurations. Electrons can be imagined as residing in fixed locations in an atomic structure known as orbitals. Each orbital can fit two electrons. The number of orbitals in each atom depends on the atom and the total number of electrons, which are reviewed in greater detail in another lesson. We'll simplify it by imagining that there are a fixed number of orbitals for each atom.
The way that electrons fill each orbital is characterized by several laws. For instance, Hund's rule states that the minor repulsion between the negatively-charged electrons will cause them to enter into separate orbitals of the same energy level before filling an orbital that already has an electron in it.
You should notice in these diagrams that electrons are shown as arrows pointing either up or down. The direction of this arrow is directly related to the electron's spin. The Pauli Exclusion Principle states that electrons filling the same orbital must have different spins because no two electrons can have the exact same quantum number. You can think of 'quantum number' as an electron's address. Because two electrons are in the same orbital, they must spin in separate directions to have a different quantum number.
Diamagnetism vs Paramagnetism
So, what does this have to do with levitating material? It turns out that the presence or absence of unpaired electrons in orbitals will give them different properties. Diamagnetic atoms have no unpaired electrons. Paramagnetic atoms have unpaired electrons.
When an orbital is filled with two electrons spinning in different directions, the total net spin of that orbital is zero. When the orbital only has one electron that is spinning, it has a net spin in that direction. If an atom has only one unpaired electron, it is still a paramagnetic atom. To be diamagnetic, all electrons must be paired.
The pairing, or lack thereof, in the atomic structure is what causes a material to behave differently when an external magnetic field is applied. In paramagnetic substances, unpaired electrons can align themselves with the external magnetic field and thus become attracted to the magnetic field. However, paramagnetic atoms do not always have magnetic behavior. Instead, this is only in response to the application of an external magnetic field. When you take away the magnetic field, the realignment of the electrons and the magnetic behavior goes away.
Because diamagnetic atoms have zero net spin and cannot align themselves to an external magnetic field, they are weakly repelled by the field, which is the cause of the pyrolytic carbon levitating above the magnets.
In summary, diamagnetism and paramagnetism are related to the number of electrons in an atom and how they fill the orbitals in the electron configuration. According to Hund's rule, the slight repulsion between two negatively charged electrons will cause them to go into orbitals of the same energy level before entering into an orbital which already contains an electron. According to the Pauli Exclusion Principle, because two electrons fill an orbital, they must have opposite spins to each other. An atom that contains any unpaired electrons is known as paramagnetic, and an atom with all paired electrons is known as diamagnetic.
Diamagnetic atoms show a weak repulsion to external magnetic fields because the electrons have zero net spin and thus cannot favorably interact with a magnetic field. Paramagnetic atoms will show a weak attraction to magnetic fields because the unpaired electrons realign themselves to meet the force of the magnetic field.
Diamagnetism & Paramagnetism: Glossary of Terms
|Diamagnetism||objects with paired electrons are repelled by an external magnetic field|
|Paramagnetism||objects with unpaired electrons are attracted to external magnetic fields|
|Hund's rule||states the minor repulsion between the negatively-charged electrons will cause them to enter into separate orbitals of the same energy level before filling an orbital that already has an electron in it|
|Pauli Exclusion Principle||states that electrons filling the same orbital must have different spins because no two electrons can have the exact same quantum number|
|Diamagnetic atoms||have no unpaired electrons|
|Paramagnetic atoms||have unpaired electrons|
After completing this lesson, the student can make it their goal to:
- Contrast diamagnetism and paramagnetism
- Recall the properties of diamagnetic and paramagnetic atoms
- Describe Hund's Rule and the Pauli Exclusion Principle
- Discuss the role of electrons in magnetic behavour
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