Thermal conductivity generally decreases when materials transition from solid to liquid states, as solids have tightly packed particles that facilitate efficient heat transfer. However, exceptions exist, such as mercury, which exhibits higher thermal conductivity in its liquid form due to its unique particle arrangement. The viscosity of a liquid also influences its thermal conductivity; more viscous liquids, like oils, conduct heat less effectively than less viscous ones, such as water. For metals, solid states typically show higher thermal conductivity, although some, like sodium and potassium, may have lower conductivity in their liquid states. Overall, the thermal conductivity of a material is influenced by its specific properties, including molecular structure and viscosity.