What impact does the number of double bonds have on van der Waals forces in fatty acids?

The number of double bonds in fatty acids affects the strength of van der Waals forces due to the impact of molecular structure and packing efficiency. Fatty acids with double bonds are typically unsaturated and contain kinks or bends in their hydrocarbon chains. These kinks hinder the close packing of fatty acid molecules.

When fatty acids are saturated (having no double bonds), they can align themselves more closely together, which facilitates stronger van der Waals interactions. In contrast, the presence of double bonds causes the fatty acid chains to be less linear and more irregular in shape. This irregularity results in decreased contact between adjacent molecules, thereby reducing the overall strength of these intermolecular forces.

Therefore, an increase in the number of double bonds corresponds to a decrease in the strength of the van der Waals forces, making the fatty acids more fluid and less stable in their aggregated forms. This is why the correct choice is that the number of double bonds decreases the strength of the van der Waals forces.