What is a non-polar molecule

In addition to polar solvents such as water, there are non-polar solvents. These are substances such as gasoline, perchlorethylene (PER) or benzene. They consist of molecules that are arranged in such a way that no centers of charge emerge on the outside. Perchlorethylene, for example, has a very symmetrical structure.

The structural formula of perchlorethylene

They are suitable for dissolving other non-polar substances such as grease (e.g. during dry cleaning). Because only non-polar solvents dissolve non-polar substances, just as only polar solvents dissolve polar substances. This is exactly where soap comes in.

Soap - mediator between the worlds

When washing, the soap plays the role of a mediator between the world of dirt (non-polar) and that of water (polar). It can be used to loosen greasy dirt in the water.

The soap is able to do this because it is a kind of hybrid molecule. It consists of a polar and a non-polar part. Polar is the small ionic (charged) group at one end of the molecule, this is called the "head". The long hydrocarbon chain of the rest of the molecule, also known as the "tail", is non-polar.

A soap anion with a polar "head", the ionic group,
and the non-polar "tail", the hydrocarbon chain.

If you put soap shavings in water, they do not dissolve down to individual molecules.

A micelle: aggregation of soap anions

Rather, they form a dispersion. The soap molecules accumulate in the water to form so-called micelles. These micelles are small spheres in which the non-polar tails of the molecules cluster together and the polar heads turn outwards. As a result, only the heads of the molecules have contact with the polar water. We also speak of hydrophilic heads, Greek for loving water, and hydrophobic, i.e. H. Water repellent tails.

This hybrid property of the soap molecules makes it possible for soap to dissolve in the water at all. If they didn't have their hydrophilic heads, they would float like fats on the water.

Many other substances, all of which are collectively referred to as surfactants, behave like soaps. They are also called surface-active substances because they mediate at the interface of polar and non-polar substances.