Diamagnetism
Definition and meaning of Diamagnetism in chemistry.
Diamagnetism is the property of a material in which an applied external magnetic field induces a weak magnetic moment that opposes the field, causing the material to be very slightly repelled by magnets.
In more detail
It arises because the magnetic field perturbs the orbital motion of paired electrons, inducing tiny circulating currents whose magnetic effect (by Lenz's law) opposes the applied field. Every atom and molecule has some diamagnetic contribution, since all electrons respond this way, but in species with unpaired electrons the much stronger paramagnetic (or ferromagnetic) attraction dominates and masks it. Diamagnetic magnetic susceptibility is negative and essentially independent of temperature, unlike paramagnetic susceptibility, which follows the Curie law and decreases as temperature rises.
Key facts
| Field | Physical Chemistry |
|---|---|
| Magnetic susceptibility | Negative (χ < 0), field-opposing |
| Origin | Paired electrons; induced orbital currents |
| Example substances | H2O, NaCl, benzene (C6H6), noble gases |
Water is diamagnetic because all its electrons are paired; this weak repulsion is strong enough that a small diamagnetic object, or even a live frog, can be levitated in a sufficiently powerful magnetic field.
Frequently asked questions
Is every substance diamagnetic?
Yes, all matter has a diamagnetic response because all electrons contribute an induced opposing moment, but in atoms or molecules with unpaired electrons this effect is overwhelmed by the much stronger paramagnetic attraction.
How is diamagnetism different from paramagnetism?
Diamagnetic substances are weakly repelled by an external magnetic field (negative, temperature-independent susceptibility), whereas paramagnetic substances, which have unpaired electrons, are weakly attracted (positive susceptibility that decreases with increasing temperature).