The Particulate Nature of Matter

All substances are made of particles.
These particles could be atoms, molecules, or ions.
These particles are in constant motion; higher the temperature, quicker the movement.
There are spaces between particles.

Matter exists in three states: Solid, Liquid, and Gas.
In solids, particles are packed closely in a fixed pattern. They can only vibrate around a fixed point.
In liquids, particles are close but can move around each other. This means liquids can flow and take shape of their containers.
In gases, particles are well separated and move quickly in all directions. Gases fill their containers completely.

Melting and Freezing: The change from solid to liquid is called melting, whereas the change from liquid to solid is freezing.
Boiling and Condensing: Liquid turning into gas is boiling or evaporation, while gas changing to liquid is called condensing.
Sublimation: Certain substances can change from solid directly to gas, bypassing the liquid state. This process is called sublimation.

The Kinetic Particle Theory explains the properties of different states of matter.
This theory considers both the movement of particles (kinetic energy) and the attraction between them.
In solids, the attractive forces are strong, keeping particles in fixed positions, so solids keep their shape.
In liquids, the attractive forces are weaker, allowing particles to move and slide past each other.
In gases, the attractive forces are very weak, letting particles move rapidly in all directions.

Diffusion is the spreading of particles from an area of high concentration to one of low concentration.
Diffusion occurs most quickly in gases, slower in liquids, and slowest in solids.
Increased temperature boosts the speed of diffusion by increasing particle motion.

Brownian Motion is the random, unpredictable movement of particles in a fluid, as observed under a microscope.
This motion is caused by the collisions of the particles with each other.
Brownian Motion is additional evidence of the particle nature of matter.