* Double Bonds: Unsaturated fatty acids have at least one double bond between carbon atoms in their hydrocarbon chain. This double bond means there are fewer hydrogen atoms attached to those carbons compared to a saturated fatty acid where all bonds are single.

* Liquid at Room Temperature: The double bonds in unsaturated fatty acids cause kinks in the molecule, making it harder for them to pack tightly together. This loose packing results in weaker intermolecular forces, leading to lower melting points. As a result, they are liquid at room temperature.

Example: Oleic acid, a common unsaturated fatty acid, has a double bond in its chain, making it liquid at room temperature.