Entropy is often described as the measure of disorder in a system and the entropy of the universe is always increasing for spontaneous process. (An argument that has unsuccessfully been used for years as an excuse for kids not to clean their rooms!) A more accurate description of entropy is the dispersal of energy and the number of energetically equivalent ways that the atoms can be arranged. However, we can relate the disorder to the dispersal of energy.
In a solid, you have a very ordered system. The components of the compound have interactions with the neighboring components and as a result have some order in the way they are arranged. This results in very low dispersal of energy.There are a limited number of ways that these atoms can be arranged that are energetically equivalent so it has a low entropy. For a gasesous compound, we lose the order that we get from the interactions of molecules and they are randomly dispersed with no interactions (i.e. no intermolecular forces) between the molecules. As a result, there are *many* energetically equivalent ways to arrange the atoms so we have more dispersal of energy and therefore higher entropy.