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Monarch Park Collegiate
Particle Theory Of Matter – Introduction
The kinetic theory of matter (particle theory) says that all matter consists of many, very
small particles which are constantly moving or in a continual state of motion. 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 visualize 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
- 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 model can be used to help explain the properties of matter and what happens during
physical changes such as melting, boiling and evaporating
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The properties of matter
Solids
Liquids
Gases
- have a definite shape
and 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
Particle Theory of Matter S.T.A.M.P.
Spaces between the individual particles are very large compared to the sizes of the
particles.
Together close, attract the most.
All particles of the same substance are identical to each other in every way. Different
substances are made of different particles.
Matter is made up of small microscopic particles.
Particles of matter are always moving.
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Changes of State (Phase Changes)
The particles of a solid or liquid possess kinetic energy (energy of motion) and
potential energy. The potential energy is due to the force of attraction between
the particles. To change the state of a substance, energy must be supplied or
removed. For example, energy must be supplied to melt ice; energy must be
removed from steam to change it into liquid water. If energy is supplied to a piece
of ice which is at zero degrees Celsius it will cause the piece of ice to melt
without causing it to change temperature. During this change of state, the
energy supplied goes into increasing the total potential energy stored in the
bonds between the molecules.
Similarly, during any change of state, it is the potential energy of the particles
which changes; the average kinetic energy (and therefore the temperature)
remains constant.