Kinetic theory of matter: all matter is composed of tiny, invisibleparticles. Particles of different substances have different sizes. Increasing temperature increases the kinetic energy of the particles.
Solids: particles have fixed positions close together. Particles can vibrate about these positions but do not have enough energy to overcome the bonds holding them together. Solids have a fixed, definite shape and volume. They are incompressible, so they transmit forces.
Melting: If the temperature is raised, particles in a solid gain kinetic energy. They vibrate more vigorously, and, if enough energy is available, they partially overcome bonds between molecules. When this happens, the solid melts and becomes a liquid. The opposite of melting is freezing.
Liquids: particles are slightly further apart than in solids- they have gained enough energy to partially overcome the bonds holding them together. Particles can move freely, so that even though a liquid has a fixed volume, it can take the shape of its container. Liquids can be compressed very slightly, but generally they are regarded as incompressible. Liquids are fluids- they can flow and transmit pressure.
Boiling: If the temperature is raised, particles in a liquid gain kinetic energy. They begin to move faster and vibrate more vigorously. If enough energy is supplied, the particles will be able to overcome intermolecular bonds and become a gas. This process is boiling; the opposite is condensation. Boiling is not the same as evaporation.
Gases: particles are widely separated and have high energy, leading to weak intermolecular bonds (we often assume there are no intermolecular bonds). Particles can move freely and randomly, so gases take the shape and volume of their container. About 99.99% of a gas’s volume is empty space. Gases are also fluids, they can flow and transmit pressure, even though in everyday terms we only think of liquids as fluids.
Volatile solids and liquids are substances which vaporise easily. Volatile substances usually have small molecules with weak intermolecular bonds that are easily overcome by a small input of energy. I2, CFC’s and other small organic molecules are all volatile.
