Magnetic Fields – Is Hydrogen Atom with a Single Unpaired Electron Diamagnetic?

electronshydrogenmagnetic fieldsquantum-spin

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).

Best Answer

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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