There are three states of matter:
Which state something is in depends on...
...temperature, pressure and type of material.
This is because temperature, pressure and type of material
affect how strong the forces of attraction between particles are
in the material.
In a solid the forces of attraction
between particles are strong. This
holds them close together in fixed
positions.
The particles do not move from
these fixed positions so they keep
a definite shape and volume.
If we drop our solid into this jar it
doesn’t change. It stays the same
shape and it stays the same
volume.
In a solid, the particles
vibrate in their positions.
How much they vibrate
depends on temperature.
The hotter they get the
more they vibrate, which
makes solids expand slightly
when heated.
In a liquid the forces of attraction
between particles are weak. This holds
them close together but they are in
random positions and they move.
The particles keep a definite
volume but not a definite
shape.
If we drop our liquid into this
jar it will flow to fill the bottom.
It has changed its shape but
not its volume.
The particles in a liquid are
moving about with random motion.
The hotter they get the faster they
move, so a liquid will expand when
heated.
In a gas the forces of
attraction between particles
are very weak.
The particles in a gas travel in
straight lines until something
changes their direction. This
means they will spread out.
If we pump our gas into this
They will expand to fill
jar it will expand to fill it.
whatever container they are in.
Gases do not keep definite
shape or volume.
To fit into a
container a gas will
change...
shape...
...and
volume.
Gases in a container are under
pressure. The smaller the container
the higher the pressure.
When they get hotter, the particles
in a gas move faster. This causes
them to expand until they have
filled all available space. Then
heating increases the pressure.
Heating a solid makes the particles vibrate more. This weakens
the forces holding the solid together.
At a certain temperature the particles have enough energy to
escape the solid. This is called the melting point.
Above the melting point the solid becomes a liquid. Heating
further makes the particles move faster, weakening the forces
between them.
At a certain temperature the particles have enough energy to
escape the liquid. This is called the boiling point.
As the particles cool they no longer have enough energy to
overcome the attraction between them.
Bonds form between the particles and they condense from gas to
liquid and freeze from liquid to solid.
It is important to know the proper names for transition between
the states of matter; melting, freezing, boiling and condensing.
The amount of energy needed
for something to change state
depends on how strong the
forces between the particles
are.
Stronger forces need more
Weaker forces need less energy
energy to break them so the
to break them so the melting
melting and boiling points are
and boiling points are low.
high.
Sometimes chemical equations will have a state symbol next to
them. Aqueous means dissolved in water.
(s) = solid
(l) = liquid
The difference between
aqueous (aq) and liquid
(l) can be shown using
table salt.
Dissolved salt has not
melted, it is aqueous.
(g) = gas
(aq) = aqueous
Here is an example of an equation showing state symbols:
Fe(s) + CuSO4(aq) → FeSO4(aq)+ Cu(s)
The copper has precipitated from an aqueous state to a solid.
You may be asked what state something is in at a certain
temperature.
Example:
Water has a melting point of 0oC and a boiling point of 100oC. What is the
state of water at 60oC?
Above the boiling point (100oC) water is a gas.
Below melting point (0oC) water is a solid.
Any temperature in between and water is a liquid.
So at 60oC water is a liquid.
Extension
•
A fourth state of matter which rarely occurs on Earth is
plasma. Plasma is electrically conductive gas. It contains free
electrons because some of the electrons have dissociated from
the gas atoms. Plasma has different properties from the other
three states of matter.
•
Some substances can go straight from a solid to a gas without
becoming a liquid in between. This is called sublimation. An
example is solid carbon-dioxide (also known as dry ice) and
carbon dioxide gas.