Paramagnetism is a property exhibited by certain substances that contain unpaired electrons in their atomic or molecular orbitals. These unpaired electrons create magnetic moments that align with an external magnetic field, causing the substance to be weakly attracted into the field. In other words, paramagnetic substances become weakly magnetized in the presence of an external magnetic field.

Key points about paramagnetism include:

1. Unpaired Electrons: Paramagnetism arises from the presence of unpaired electrons in an atom, ion, or molecule. These unpaired electrons have spin angular momentum, which gives rise to magnetic moments.
2. Alignment in Magnetic Field: When a paramagnetic substance is placed in an external magnetic field, the unpaired electrons align their magnetic moments with the field direction. This alignment enhances the overall magnetic effect of the substance.
3. Temporary Magnetism: Paramagnetism is a temporary effect. Once the external magnetic field is removed, the random thermal motion disrupts the alignment of the magnetic moments, and the substance loses its magnetization.
4. Curie’s Law: The magnetic susceptibility (χ) of a paramagnetic substance is directly proportional to the number of unpaired electrons and the strength of the external magnetic field. This relationship is described by Curie’s law: χ = C/T, where C is the Curie constant and T is the temperature in Kelvin.
5. Temperature Dependence: The degree of paramagnetism decreases with decreasing temperature due to the thermal energy’s influence on the alignment of magnetic moments. At very low temperatures, paramagnetic substances may exhibit antiferromagnetic or ferromagnetic behavior instead.
6. Examples: Atoms or ions with unpaired electrons, such as the transition metals, certain lanthanides and actinides, and some organic radicals, can exhibit paramagnetism. Oxygen gas (O2) is another example of a paramagnetic substance due to its two unpaired electrons.
7. Magnetic Susceptibility: Magnetic susceptibility measures the extent to which a substance becomes magnetized in an external magnetic field. A positive magnetic susceptibility indicates paramagnetism.

Paramagnetism is often observed in coordination complexes containing transition metal ions with unpaired d electrons. The presence of unpaired electrons in these complexes gives rise to magnetic properties that can be analyzed through techniques like magnetic susceptibility measurements and electron paramagnetic resonance (EPR) spectroscopy.