The particles in a solid are packed very closely together in a rigid, orderly arrangement. They are held together by the attractive forces that act
between all particles of matter. Solids, therefore, have fixed volumes and
shapes. In the solid state, particles cannot break away from their fixed
position; they can only vibrate in place.
The particles that make up a liquid move more rapidly than those in a solid
do. This causes the particles in the liquid to overcome some of the
attractive forces between them, and the particles can slide freely around
each other.
The particles of a gas are very far apart and move rapidly compared to
particles in solids or liquids. At these distances, the attractive forces
between gas particles have a lesser effect than they have on particles in
liquids and solids. In general, the volume of a liquid or solid increases
greatly when it forms a gas. However, the density of the gaseous state of
most substances is approximately one-thousandth the density of the liquid
state.
Plasma is a gas in which the particles have so much energy that they
become electrically charged. Plasma is the most common state of matter in
the universe, with more than 99.99% of observable matter in the universe
being plasma. Most of the matter of the sun is plasma. Stars and lightning
are also examples of plasma. However, this state is not experienced in the
physical and chemical changes we encounter every day on Earth.