MCAT Content / Electronic Structure / Paramagnetism And Diamagnetism

Paramagnetism and diamagnetism

Topic: Electronic Structure

A diamagnetic atom has a net spin of zero as all electrons are paired up in its orbitals. A paramagnetic atom has unpaired electrons, resulting in a non-zero net spin.

Diamagnetism

Any time two electrons share the same orbital, their spin quantum numbers have to be different. In other words, one of the electrons has to be “spin-up,”s = +(½) while the other electron is “spin-down,” with s = -(½). Since electrons in the same orbital always have opposite values for their spin quantum numbers (s), they will always end up cancelling each other out. In other words, there is no leftover spin in an orbital that contains two electrons.

Electron spin is very important in determining the magnetic properties of an atom. If all of the electrons in an atom are paired up and share their orbital with another electron, then the total spin in each orbital is zero, and the atom is diamagnetic. Diamagnetic elements are not attracted to a magnetic field, but rather are slightly repelled.

Paramagnetism

Electrons that are alone in an orbital are called paramagnetic electrons. If an electron is alone in an orbital, the orbital has a net spin, because the spin of the lone electron does not get cancelled out. If one orbital has a net spin, the entire atom will have a net spin. Therefore, an atom is considered to be paramagnetic when it contains at least one paramagnetic electron. In other words, an atom could have ten paired (diamagnetic) electrons, but as long as it also has one unpaired (paramagnetic) electron, it is still considered a paramagnetic atom.o

Just as diamagnetic atoms are slightly repelled from a magnetic field, paramagnetic atoms are slightly attracted to a magnetic field. Paramagnetic properties are due to the realignment of the electron paths caused by the external magnetic field. Paramagnets do not retain any magnetization in the absence of an externally applied magnetic field, because thermal motion randomizes the spin orientations. Stronger magnetic effects are typically only observed when d- or f-electrons are involved, notably in the transition metals like iron.

Practice Questions

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Key Points

• Any time two electrons share the same orbital, their spin quantum numbers have to be different. Whenever two electrons are paired together in an orbital, or their total spin is 0, they are diamagnetic electrons. Atoms with all diamagnetic electrons are called diamagnetic atoms.

• A paramagnetic electron is an unpaired electron. An atom is considered paramagnetic if even one orbital has a net spin. An atom could have ten diamagnetic electrons, but as long as it also has one paramagnetic electron, it is still considered a paramagnetic atom.

• Diamagnetic atoms repel magnetic fields. The unpaired electrons of paramagnetic atoms realign in response to external magnetic fields and are therefore attracted. Paramagnets do not retain magnetization in the absence of a magnetic field, because thermal energy randomizes electron spin orientations.


Key Terms

diamagnetic: materials that create an induced magnetic field in a direction opposite to an externally applied magnetic field and are therefore repelled by the applied magnetic field.

paramagnetic: materials that are attracted by an externally applied magnetic field and form internal, induced magnetic fields in the direction of the applied magnetic field.

quantum numbers: used to describe characteristics of electrons

electron spin:  is an intrinsic form of angular momentum carried by electrons.



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