Final answer:
The liquid state of matter consists of particles with enough energy to move around each other while maintaining close contact, giving liquids a fixed volume but no fixed shape. They differ from gases, as they do not expand to fill their containers, and exhibit viscosity, which is resistance to flow.
Step-by-step explanation:
The liquid state of matter is characterized by a collection of particles—atoms or molecules—that maintain close contact while possessing enough energy to move around each other within a confined space. This dynamic behavior allows liquids to acquire the shape of their containers, although they retain a fixed volume. The movement of these particles also makes liquids and gases fluid, as they can flow and yield to shearing forces, unlike solids. However, liquids differ from gases in that their volumes are relatively unaffected by changes in temperature and pressure, and they do not expand to fill their containers. Furthermore, liquids can experience changes of state: when heated, they can transition to gases, and when cooled, they solidify into solids. These transformations are physical changes that do not alter the chemical composition of a substance.
Liquids demonstrate intermolecular interactions which help maintain a definite volume and prevent the particles from escaping the liquid boundary, yet these interactions are not strong enough to hold the particles in a fixed position, allowing for fluid movement. The extent to which liquids flow is also influenced by their viscosity, which is a measure of the liquid's resistance to flow.