Final answer:
Saturated fats have straight chains that pack tightly and are usually solid at room temperature, while unsaturated fats have kinked chains due to double bonds, leading to weaker intermolecular forces and a liquid state at room temperature.
Step-by-step explanation:
The physical structure and appearance of fats are significantly influenced by whether they are saturated or unsaturated. Saturated fatty acids have a cylindrical shape that allows them to pack tightly together, which typically results in a solid state at room temperature. This structure is due to their carbon chains lacking double bonds, leading to straight chains that can stack closely in a crystal lattice, maximizing intermolecular dispersion forces which give them higher melting points.
Conversely, unsaturated fatty acids contain at least one double bond in the cis configuration, introducing a kink into the chain. These kinks prevent the fatty acids from packing as tightly as saturated ones, resulting in a smaller contact area between molecules and weaker intermolecular forces. As a consequence, unsaturated fats tend to have lower melting points and are usually liquids at room temperature. The presence of this double bond and the geometric kink it creates is the key factor that affects the state of the fat.