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I know that paramagnetism is caused because of the net magnetic dipole moment of an atom with unpaired electrons. On the other hand, all substances exhibit diamagnetism, but the effect is weak and mostly overshadowed by effects like paramagnetism. It is also said that substances with paired electrons in their orbitals are the ones that exhibit diamagnetism. But a hydrogen atom only has one electron in total. Does it show diamagnetism (even if it is weak)? How is pairing of electrons related to diamagnetism?

(I can understand how unpaired electrons causes paramagnetism, but I'm not clear on how pairing of electrons can generate another form of magnetism).

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Whenever you have an atomic dipole, in the presence of an external magnetic field, magnetization will occur.

Hydrogen is not usually called paramagnetic since monoatomic hydrogen is very unstable and hydrogen atoms will combine to form H$_2$ (meaning the magnetic moments become quenched - all the spins become paired). Hydrogen (molecular hydrogen) is therefore diamagnetic.

But paramagnetic substances require at least one unpaired electron (since the net magnetic moment of the electrons do not add up to zero). This is because in the presence of a magnetic field, the atomic dipoles align along the field (albeit this magnetization is weak). So atomic hydrogen is in fact paramagnetic because it has an unpaired electron.

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  • $\begingroup$ When a substance is brought to an external magnetic field, a current that will generate an opposing magnetic field is produced by the electrons. This is how diamagnetism is usually explained. But why only paired electrons generate such a current/opposing magnetic field? $\endgroup$
    – Sasikuttan
    Oct 21, 2021 at 5:45
  • $\begingroup$ I thought I explained it. A diamagnetic substance has no magnetic moment because all the electrons are paired. $\endgroup$
    – joseph h
    Oct 21, 2021 at 5:54
  • $\begingroup$ Please correct me if I'm wrong => All electrons in a substance, BE IT PAIRED OR UNPAIRED, will generate an opposing magnetic field in presence of an external magnetic field. But in those substances where electrons are paired, this effect will be more pronounced. Because, when there are unpaired electrons, the substance will have net magnetic moment, which causes the substance to be paramagnetic or ferromagnetic - and this overshadows diamagnetic properties of the substance. Correct? $\endgroup$
    – Sasikuttan
    Oct 21, 2021 at 6:03
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    $\begingroup$ YES! :) that is correct. Cheers! $\endgroup$
    – joseph h
    Oct 21, 2021 at 6:06

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