Kinectic Particle Theory

The kinetic particle theory states that all matter is made up of tiny particles that are in constant random motion and constantly collide with each other.(Particles is an umbrella term, and atoms are under the category of particles.) The degree to which the particles move is determined by the amount of energy they have and their relationship to other particles. The particles might be atoms, molecules or ions. Use of the general term 'particle' means the precise nature of the particles does not have to be specified.
Particle theory helps to explain properties and behaviour of materials by providing a model which enables us to visualise what is happening on a very small scale inside those materials. As a model it is useful because it appears to explain many phenomena but as with all models it does have limitations.

Solids, liquids and gases

In solids the particles	In liquids the particles	In gases the particles
are held tightly and packed fairly close together - they are strongly attracted to each other o are in fixed positions but they do vibrate	are fairly close together with some attraction between them are able to move around in all directions but movement is limited by attractions between particles	have little attraction between them are free to move in all directions and collide with each other and with the walls of a container and are widely spaced out

Fig 1 Particles in solids, liquids and gases

The properties of matter

Solids	Liquids	Gases
have a definite shape maintain that shape are difficult to compress as the particles are already packed closely together are often dense as there are many particles packed closely together	do not have a definite shape flow and fill the bottom of a container. They maintain the same volume unless the temperature changes are difficult to compress because there are quite a lot of particles in a small volume are often dense because there are quite a lot of particles in a small volume	do not have a definite shape expand to fill any container are easily compressed because there are only a few particles in a large volume are often low density as there are not many particles in a large space

Kinetic Particle Theory - how it explains changes of states

For example:

During Melting,

1.     When a solid is heated, heat energy is absorbed by the particles.

2.     The heat energy is then converted into kinetic energy and the particles begin to vibrate faster.

3.     At the melting point, the particles vibrate vigorously enough to overcome their forces of attraction (break away from their fixed positions). Hence melting occurs.

-      * During melting, the temperature remains constant at the melting point because the heat absorbed is used to overcome the forces of attraction between the particles.

During Freezing,

1.     When a liquid is cooled, the particles lose kinetic energy. They move more and more slowly.

2.     At the freezing point the particles can only vibrate about their fixed positions and hence a solid is formed.

Sublimation:

o   Some sublimation such as iodine, ammonium chloride, mothball and dry ice(solid carbon dioxide) sublime on gentle heating. The solid changes to a gas without melting.

o   Sublimation occurs because the particles at the surface of the solid have enough energy to break away from the solid and escape as a gas.

Evaporation:

o   Evaporation is a change from the liquid to the gaseous state that occurs at any temperature below the boiling point.

o   Evaporation occurs slowly and takes place only at the surface of the liquid.

o   Evaporation occurs because the particles at the surface of the liquid have enough energy to break away from the liquid and escape as a gas.

o   During evaporation, the particles left behind have a lower kinetic energy and therefore cause cooling effect.

o   Further explaining:

-      Water is made up of many molecules that are in constant, random motion.

-      These molecules collide with each other to gain or lose kinetic energy from or to other molecules.

-      The molecules nearer to the surface of the water and have high enough kinetic energy will be able to change from liquid to gaseous state.

-      Since the molecules with higher kinetic energy have moved out of the water, the average kinetic energy of the water drops which in turns means that the temperature of water will drop as well.

• have a definite shape
• maintain that shape
• are difficult to compress as the particles are already packed closely together
• are often dense as there are many particles packed closely together

• do not have a definite shape
• flow and fill the bottom of a container. They maintain the same volume unless the temperature changes
• are difficult to compress because there are quite a lot of particles in a small volume
• are often dense because there are quite a lot of particles in a small volume

• do not have a definite shape
• expand to fill any container
• are easily compressed because there are only a few particles in a large volume
• are often low density as there are not many particles in a large space