in a solid, particles are bonded together rigidly, all particles held in place. we know that when we heat a solid, we can turn it into a liquid; this is because when we give the solid energy in the form of heat, some of the bonds between particles that keep the structure rigid, break apart. this energy increase has made the particles less attracted to eachother; in this situation, some bonds remain, while some are broken, and the bonds are constantly breaking and reforming. this is what gives liquids their fluid properties (among other things) but is also what differentiates them from gasses; in a gas, no bonds remain between particles.
