Fatty acids are merely carboxylic acids with long hydrocarbon chains. The hydrocarbon chain length may vary from 10-30 carbons (most usual is 12-18). The non-polar hydrocarbon alkane chain is an important counter balance to the polar acid functional group. In acids with only a few carbons, the acid functional group dominates and gives the whole molecule a polar character. However, in fatty acids, the non-polar hydrocarbon chain gives the molecule a non-polar character.
Thumbnail: A ball-and-stick diagram of arachidonic acid. Image used with permission (Public Domain; ). Arachidonic acid is a polyunsaturated fatty acid present in the phospholipids of membranes of the body's cells, and is abundant in the brain, muscles, and liver.