What characterizes a paramagnetic substance?

A paramagnetic substance is characterized primarily by its unpaired electrons. These unpaired electrons create a magnetic moment, which allows the substance to be weakly attracted to an external magnetic field. When an external magnetic field is applied, the magnetic moments of the unpaired electrons align with the field, resulting in a net attraction.

This weak attraction is what distinguishes paramagnetic materials from diamagnetic materials, which contain all paired electrons and are actually repelled by magnetic fields. The presence of unpaired electrons is crucial for the paramagnetic property, as it is the unpaired electrons that respond to the magnetic field.

In contrast, substances that are strongly repelled by a magnetic field are typically diamagnetic, while those that retain permanent magnetism are classified as ferromagnetic. Therefore, the defining feature of paramagnetic substances is their weak attraction to an external magnetic field due to unpaired electrons.