States of Matter - States of matter and changes of state

The Kinetic Particle Theory states that all matter is made of tiny particles (atoms, molecules, or ions) that are in constant, random motion.

In a Solid, particles are packed closely together in a regular lattice arrangement. They vibrate about fixed positions and have strong intermolecular forces of attraction.

In a Liquid, particles are close together but arranged randomly. They can move and slide past each other, allowing liquids to flow and take the shape of their container.

In a Gas, particles are far apart and move rapidly and randomly in all directions. Intermolecular forces are negligible, and gases are easily compressed.

Melting ($S \rightarrow L$) and Boiling ($L \rightarrow G$) are endothermic processes where energy is absorbed to overcome forces of attraction between particles.

Freezing ($L \rightarrow S$) and Condensation ($G \rightarrow L$) are exothermic processes where energy is released as particles form stronger bonds/attractions.

During a change of state, the temperature remains constant (represented by a plateau on a heating/cooling curve) because the energy is used to break or form bonds rather than changing the average kinetic energy ($E_k$).

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration due to their random motion. The rate of diffusion is inversely proportional to the relative molecular mass ($M_r$).

Brownian Motion provides evidence for the kinetic particle theory; it is the random jerky motion of visible particles (like pollen or smoke) caused by collisions with invisible, fast-moving air or water molecules.