Kinetic Theory (Cambridge O Level Chemistry)

Solids

• Solids have a fixed volume and shape and they have a high density
• The atoms vibrate in position but can’t change location
• The particles are packed very closely together in a fixed and regular pattern

Liquids

• Liquids also have a fixed volume but adopt the shape of the container
• They are generally less dense than solids (an exception is water), but much denser than gases
• The particles move and slide past each other which is why liquids adopt the shape of the container and also why they are able to flow freely

Gases 

• Gases do not have a fixed volume and fill their container
• Gases have a very low density
• Since there is a lot of space between the particles, gases can be compressed into a much smaller volume
• The particles are far apart and move randomly and quickly (around 500 m/s) in all directions
• They collide with each other and with the sides of the container (this is how pressure is created inside a can of gas)

Summary of the Properties of Solids, Liquids and Gases

State	Solid	Liquid	Gas
Density	High	Medium	Low
Arrangement of particles	Regular pattern	Randomly arranged	Randomly arranged
Movement of particles	Vibrate around fixed positions	Move around each other	Move quickly in all directions
Energy of particles	Low energy	Greater energy	Highest energy
2D diagram