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Chemistry > Solids, Liquids and Gases

Pretty much everything on Earth exists as a solid, a liquid or a gas. These three states are commonly known as the 'three states of matter'.

Materials can change state if heated or cooled.

Water for example is a liquid but can be turned into a gas (water vapour) through heating. This process is called 'Evaporation'

The process of cooling which changes liquid water into solid ice is called 'Freezing' The process of cooling which changes water vapour (gas) back into water (liquid) is called 'Condensing'

When solid ice is converted into liquid water, this is called 'Melting'

The processes which can take place are illustrated below (see fig 1):

Fig 1: Changing States
Fig 1:
Changing States


Gases have no fixed volume, they simply fill then container they are in.

The attractive forces between particles are very small and so they are free to move in any direction. These particles move around in a random unordered way colliding with each other and the walls of the container.

As the temperature increases, the particles in a gas move around faster as they gain kinetic energy.


Liquids have a fixed volume at a given temperature. As this temperature increases, the particles gain kinetic energy and so move faster, colliding with each other more frequently.

Compared to gases, the particles exert a greater force of attraction on each other, although this is still relatively weak compared to particles in solids.

Particles are arranged at random but are closer together than those of a gas. Sometimes clumps of particles may cling together temporarily.


Solids have a fixed volume and shape at a given temperature unless deformed by an external force. Particles are packed together with strong forces of attraction acting between them and are arranged in a uniform ordered arrangement.

Particles are held together too tightly for them to move although they can vibrate about their position.

As temperature increases, the particles vibrate faster and faster as they gain kinetic energy.

Solids, Liquids and Gases summary and notes:

  Greatest   Least
Density Order
Solids Liquids gases
Ease of Flow
Gases Liquids Solids
Ease of Compression
Gases Liquids Solids
  • Both gases and liquids can be described as 'fluids' as they can both flow readily.
  • Diffusion occurs at a more rapid rate in gases as there is much more space in which the particles are free to move about.
  • The sticky properties of viscous liquids are such because the forces of attraction between molecules are greater.
  • Diffusion in solids is virtually impossible because of the lack of empty space between molecules.
Scientists have recently discovered what is often called the forth state of matter in 'Plasma'. Plasma is, put simply, an ionised gas; a gas that has been energized to the point that some of the electrons break free from, but travel with, their nucleus. The effect can be seen in 'plasma balls' available through lab suppliers and other highstreet shops. Although the principle is generally not covered until 'A' level science studies and beyond, many schools have plasma balls which may get used for open and induction days.