dipôles

A dipole is a fundamental concept in physics and chemistry that refers to a system consisting of two equal and opposite charges separated by a small distance. The term originates from the Greek words *di-* (meaning "two") and *-pole* (referring to a pole of a magnet or charge). Dipoles are prevalent in various fields, including electrostatics, molecular physics, and electrical engineering.

In electrostatics, a dipole consists of two point charges of equal magnitude but opposite sign (positive and negative). The separation between the charges defines the dipole moment, a vector quantity denoted by **p**, calculated as the product of the charge magnitude (*q*) and the distance (*d*) between them, directed from the negative to the positive charge. The SI unit of dipole moment is the coulomb-meter (C·m). Dipoles create non-uniform electric fields, influencing surrounding charged particles and other dipoles.

At the molecular level, polar molecules exhibit permanent dipole moments due to an uneven distribution of electron density. This occurs when atoms within a molecule have differing electronegativities, causing a shift in electron cloud distribution. Examples include water (H₂O) and hydrogen fluoride (HF), where oxygen and fluorine, being more electronegative than hydrogen, attract shared electrons more strongly, creating a net dipole moment. Nonpolar molecules, such as carbon dioxide (CO₂), have symmetrical charge distributions, resulting in a net dipole moment of zero.

Dipoles also play a critical role in electrical engineering, particularly in capacitors and antennas. In capacitors, the alignment of dipoles in dielectric materials enhances charge storage by reducing the electric field between plates. In antennas, dipoles are fundamental structures that emit or receive electromagnetic waves when driven by alternating currents.

Induced dipoles occur in nonpolar molecules when exposed to an external electric field, causing temporary charge separation. This phenomenon is key in phenomena like van der Waals forces, which contribute to intermolecular interactions in solids and liquids. Understanding dipoles aids in explaining properties such as solubility, boiling points, and the behavior of materials in electric fields.