Solids, Liquids & Gases (OCR A Level Physics): Revision Note

Solids, Liquids & Gases

• The three states of matter are solid, liquid and gas

Water has three states of matter; solid ice, liquid water and gaseous steam. The difference between each state is the arrangement of the particles

Kinetic Model for Solids, Liquids & Gases

• The kinetic theory of matter is a model that attempts to explain the properties of the three states of matter

  • In this model, particles are assumed to be small solid spheres

Solids

• Particles in solids:

  • Are held together by strong intermolecular forces

  • Are closely packed

  • Are arranged in a fixed pattern (lattice structure)

  • Can only vibrate about their fixed positions

  • Have low energies compared to particles in liquids and gases

• As a result of the arrangement and behaviour of their particles, solids:

  • Have a fixed shape (although some solids can be deformed when forces are applied)

  • Have a fixed volume

  • Are very difficult to compress

  • Have higher densities than liquids and gases

Liquids

• Particles in liquids:

  • Are held together by weaker intermolecular forces compared to the forces between particles in solids

  • Are closely packed

  • Are randomly arranged (i.e. there is no fixed pattern)

  • Can flow past each other

  • Have higher energies than particles in solids, but lower energies than gas particles

• As a result of the arrangement and behaviour of their particles, liquids:

  • Do not have a fixed shape and take the shape of the container they are held in

  • Have a fixed volume

  • Are difficult to compress

  • Have lower densities than solids, but higher densities than gases

Gases

• Particles in gases:

  • Have negligible intermolecular forces between them

  • Are far apart (the average distance between the particles is ∼10 times greater than the distance between the particles in solids and liquids)

  • Are randomly arranged

  • Move around in all directions at a variety of speeds, occasionally colliding with each other and with the walls of the container they are in

  • Are negligible in size compared to the volume occupied by the gas

  • Have higher energies than particles in solids and liquids

In a gas, particles can move around freely in all directions (shown by the arrows).

• As a result of the arrangement and behaviour of their particles, gases:

  • Do not have a fixed shape and take the shape of the container they are held in

  • Do not have a fixed volume and expand to completely fill the available volume

  • Can be compressed

  • Have the lowest densities (∼1000 times smaller than the densities of solids and liquids)