Fat molecules are composed of three fatty acids bonded to a glycerol molecule. A fatty acid is a carboxylic acid group with a hydrocarbon chain attached. Fat molecules are collectively known as triglycerides because of their composition.
The specific name and classification of a fat molecule is derived from the type of hydrocarbons attached to it. Saturated fat molecules have hydrocarbon chains comprised entirely of single bonded carbons. They are solid at room temperature and are usually found in the fat stores of animals. Unsaturated fat molecules contain at least one double bond somewhere between the carbons of the hydrocarbon chains. They are liquid at room temperature and are typically found in the form of oils found in plants.
Other physical and chemical properties, besides the state of matter, of fat molecules also differ significantly depending on whether it is a saturated or unsaturated fat. Saturated fats are fairly linear molecules that are found stacked on top of each other. This increases their melting points and makes some harder to breakdown.
Unsaturated fats contain a bend in their molecular structure because of the double bond or bonds found in their hydrocarbon chains. This prevents the molecules from stacking up together and gives them a lower melting point. Because fats can only release energy if they are broken down, it is better to have a structure that is less restricted by intermolecular forces and surrounding molecules, which is why unsaturated fats are considered healthier.