In a liquid, the particles have more thermal energy compared to those in a solid. This increased energy allows the particles to overcome some of the forces that hold them together, enabling them to move around each other. As a result, liquids have a definite volume but take the shape of their container. The particles in a liquid are still close together, but they can flow, allowing liquids to be poured and to conform to the shape of different containers.
In a gas, the particles have even more thermal energy. They are spaced far apart and move rapidly and freely, which allows gases to expand and fill the entire volume of their container. Because the particles in a gas have so much energy, they can move great distances without being influenced by one another, leading to a lack of definite shape or volume. Gases will take the shape and volume of whatever space they occupy.
As thermal energy changes in a substance, so does its state of matter. For example, heating a solid can provide the thermal energy needed for it to transition into a liquid (melting), and further heating can transform the liquid into a gas (evaporation). Conversely, cooling a gas can lead to condensation (turning into a liquid), and further cooling can solidify it (freezing). Thus, thermal energy plays a crucial role in determining the behavior and arrangement of particles in different states of matter.