Why are lipids insoluble in water

To understand the phenomenon that results into the hydrophobic behavior of lipids, it is necessary to know the basics of the atomic make up of these two entities — lipids and water. Water, chemically known as H2O, comprises of a single oxygen atom and a couplet of hydrogen atoms, attached to each other through what is known as hydrogen bonding. The oxygen nucleus, being bigger in size than that of the hydrogen atom, is more electronegative. In simpler words, it has greater ability to attract electrons towards itself. These electrons carry negative charge, and the result of the complete transaction is that oxygen atom acquires a negative charge that is sufficient to attract the oppositely charged hydrogen atoms. This is the gist of the hydrogen bonding in water.

On the other hand, lipids are actually long chain hydrocarbons. Carbon atoms and hydrogen atoms have similar electronegativity which results into the formation of these long chains of a carbon atom being complemented by hydrogen atoms. These chains may take either a saturated or an unsaturated form. A saturated chain comprises a single bond between the different carbon bonds whereas the unsaturated carbon atoms are attached through double to triple bonds. This molecular structure is called non polar, whereas that of water is called polar. The polar bonds are much more energetically stable and viable; hence, the water molecules exhibit extreme affinity for each other. In stark contrast, the hydrocarbon chains are not able to establish a substantial degree of affinity with the water molecules, and hence, do not mix up. Thus, the attribute of the insolubility of lipids in water is a result of the greater adhesiveness between the water molecules than that between the molecules of water and the lipid substance.

Some chemical editing may help in overcoming this situation. By the introduction of a hydrophilic element in the chemical blueprint of lipids, they acquire a highly adhesive tail end which displays appreciable affinity with water molecules. Carboxyl and phosphate groups are the major hydrophilic components. In fact, this is precisely the phenomenon is evident in the working of soaps.