Why do polar molecules have permanent dipoles



A Dipole molecule is an electrically neutral molecule in which the electrons are distributed asymmetrically and therefore a dipole is formed. The centers of gravity of the positive and negative charges do not coincide locally, so that the molecule has a polarity with a positive and a negative pole, it is a polar atomic bond. In addition to polar atomic bonds, free electron pairs also contribute to polarity.

The product of the charge difference and the charge spacing is called the dipole moment.

The water molecule is the best known example of a dipole molecule. In addition to two polar H-O bonds, two lone pairs of electrons also contribute to the dipole moment.

In general, it can be said that molecules with an asymmetrical structure and a ΔEN greater than 0.4 and less than 1.7 appear as a dipole, i.e. H. they are electrically neutral to the outside, but have a dipole moment.

However, the limits are 0 here < δen="">< 1,7="" als="" richtwerte="" anzusehen,="" da="" es="" hier="" auch="" fälle="" gibt,="" die="" dem="" widersprechen.="" zum="" beispiel="" hat="" die="" bindung="" c-h="" (kohlenstoff-wasserstoff)="" ein="" delta-en="" von="" 0,4,="" hat="" aber="" trotz="" eines="" asymmetrischen="" aufbaus="" kein="" dipolmoment.="" deswegen="" wirken="" zwischen="" alkanen="" und="" ähnlichen="" verbindungen="" auch="" van-der-waals-kräfte="" und="" nicht="" dipol-dipol-wechselwirkungen.="" dies="" lässt="" sich="" leicht="" an="" den="" siedepunkten="" von="" alkanen="" feststellen.="" kohlenstoffdioxid="" als="" beispiel="" für="" ein="" symmetrisches="" molekül="" mit="" δen="1,0" hat="" ebenfalls="" kein="" dipolmoment.="">

On the other hand, there are also compounds such as aluminum chloride with ΔEN = 1.5. This actually indicates a molecule. But if you put it in water, you can clearly detect ions.

Category: Chemical Bond