Why do linear molecules tend to be less water-soluble?

Linear molecules tend to be less water-soluble primarily because they have more surface area that is non-polar. In many linear molecules, the arrangement of atoms creates regions that lack polarity, meaning they do not interact favorably with water, which is a polar solvent. Water molecules are capable of forming strong hydrogen bonds with other polar molecules or with polar functional groups.

When a linear molecule has extensive non-polar regions, it cannot participate effectively in these interactions. This results in a decreased tendency for these molecules to dissolve in water because solubility often requires the solute to interact favorably with the solvent. Therefore, a greater surface area dedicated to non-polar character reduces the overall solubility of the linear molecule in a polar medium like water.

While having fewer polar groups, being larger in molecular weight, or being gaseous can also influence solubility, they don't primarily account for the trend observed in linear molecules. The extensive non-polar area is a key factor that reduces their interaction with water, thus lowering their solubility.