Dipoolmomenti

Dipoolmomenti, often referred to as dipole moments in physics and chemistry, describe the separation of positive and negative charges within a system. They are vector quantities that indicate how polar a molecule or charge distribution is.

For a discrete set of charges qi located at positions ri, the dipole moment μ is given by μ = ∑ qi ri. In continuous charge distributions, μ = ∫ r ρ(r) d^3r, where ρ(r) is the charge density. In neutral systems, the dipole moment arises from spatial separation of charge rather than a net charge, and its direction points from negative to positive charge.

The magnitude is expressed in Debye in chemistry (1 Debye ≈ 3.33564×10−30 C·m); in physics, SI units of coulomb-meter are used. The dipole moment is sensitive to molecular geometry and electronic distribution, and it is a key indicator of polarity. It influences interactions with electric fields, solvents, and other dipoles, and it affects dielectric properties, solvation behavior, and reactivity. In molecules, the overall dipole moment is the vector sum of bond dipoles and lone-pair contributions for the given geometry.

Measurement and computation: dipole moments can be determined from rotational spectroscopy of gases or dielectric constant measurements, and they are commonly estimated in quantum chemistry by μ = ⟨ψ| ∑ qi ri |ψ⟩, with ab initio or DFT methods used to optimize geometry and electron distribution. Examples of typical values include H2O ≈ 1.85 D, HCl ≈ 1.08 D, CO ≈ 0.112 D, while linear symmetric molecules like O2 have near-zero dipole moments.

Applications span polarity classification, solvent effects, spectroscopy selection rules, and the study of intermolecular forces.