Kinetic Theory (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

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, like liquids, take up the shape of the 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

	Solid	Liquid	Gas
Diagram
Arrangement of particles	Regular arrangement	Randomly arranged	Randomly arranged
Movement of particles	Vibrate about a fixed position	Move around each other	Move quickly in all directions
Closeness of particles	Very close	Close	Far apart
Density	High	Medium	Low
Energy of particles	Low energy	Greater energy	Highest energy