2. Whatis
everything
madefrom?
Everything is made of matter.
There are three forms, or states, of matter the solid
state, the liquid state and the gaseous state.
This means that everything is made up from materials
that are a solid, a liquid or a gas.
4. Solid
A solid has a definite mass.
A definite shape.
Its volume does not change.
It does not flow and it is hard to compress (squash) it.
5. Liquid
A liquid has a definite mass.
Its volume does not change.
It is hard to compress but it flows easily.
The shape of the liquid varies and depends on the
shape of the container holding it.
6. Gas
A gas has a definite mass.
Its volume can vary.
It takes up the shape of the container holding it.
It flows easily and it is easy to compress.
7. Theparticle
theoryof
matter
The particle theory states that matter is made from
particles.
The particles are so tiny that they cannot be seen with
the naked eye.
Different substances are made from different particles
and the particles have different sizes.
The particles are atoms and molecules.
9. Theparticlesin
solids
In solids, strong forces hold the particles together in a
three-dimensional structure.
In many solids, the particles form an orderly
arrangement called a lattice.
The particles in all solids move a little.
They do not change position but vibrate to and fro
about one position.
10. Theparticlesin
liquids
In liquids, the forces that hold the particles together
are weaker than in solids.
The particles in a liquid can change position by sliding
over each other.
11. Theparticlesin
gases
In gases, the forces of attraction between the particles
are very small.
The particles can move away from each other and
travel in all directions.
When they hit each other or the surface of their
container they bounce and change direction.
12. Whenmatter
changesstate
The state of matter of a substance can be changed.
This kind of change is called a physical change. It is a
reversible reaction.
This means that the reaction can go forwards and also
backwards, as we shall see.
A physical change of state can be brought about by
heating or by cooling.
13. Melting
If a solid is heated enough, it loses its shape and starts
to flow.
This change is called melting.
The solid turns into a liquid.
The temperature at which melting takes place is called
the melting point.
This can be found by heating a solid and recording its
temperature.
When the temperature remains constant or steady, the
melting point of the solid has been reached.
For example, butter or ghee melts in a pan during
cooking and chocolate can melt in your pocket.
14. Melting
(Particletheory)
When a solid is heated, the heat provides the particles
with more energy.
The energy makes the particles vibrate more strongly
and push each other a little further apart.
The solid expands.
If the solid is heated further, the energy makes the
particles vibrate so strongly that they slide over each
other and become a liquid.
During the time from when the solid starts to melt
until it has completely turned into a liquid, its
temperature does not rise.
All the heat energy is used to separate the particles so
that they can flow over one another.
15. Freezing
Freezing is the reverse of melting.
It is the changing of a liquid into a solid.
The temperature at which this takes place is called the
freezing point.
It is the same temperature as the melting point of the
substance.
For example, when molten wax runs down the side of
a candle it freezes and becomes a solid before it reaches
the bottom.
16. Freezing
(Particletheory)
If a liquid is cooled sufficiently the particles lose so
much energy that they can no longer slide over each
other.
The only movement possible is the vibration to and fro
about one position in the lattice.
The liquid has become a solid.
17. Evaporation
A solid turns into a liquid at one definite temperature
(the melting point) but a liquid turns into a gas over a
range of temperatures.
For example, a drop of water can turn into a gas
(known as water vapour) at room temperature of about
20°C while outside a puddle dries up in the warmth
from the Sun.
The process by which a liquid changes into a gas over
a range of temperatures is called evaporation.
The gas escapes from the surface of the liquid.
18. Evaporation
(Particletheory)
If the temperature of the liquid is higher, it evaporates
faster.
If the air above the liquid does not already have a lot of
vapour in it, the liquid evaporates faster.
The particles in a liquid have different amounts of
energy.
The particles with the most energy move the fastest.
High-energy liquid particles near the surface move so
fast that they can break through the surface and
escape into the air, forming a gas.
19. Boiling
When a liquid reaches a certain temperature, it forms
a gas inside it.
The gas makes bubbles, which rise to the surface and
burst into the air.
This process is called boiling.
The temperature at which it takes place is called the
boiling point.
If the boiling liquid is heated more strongly, its
temperature does not rise but it boils more quickly.
20. Boiling
(Particletheory)
When a liquid is heated, all the particles receive more
energy and move more quickly.
The fastest- moving particles escape from the liquid
surface or collect in the liquid to form bubbles.
The bubbles rise to the surface and burst open into the
air.
The fast-moving particles released from the liquid form
a gas.
21. Condensation
If a gas is cooled down far enough, it turns into a liquid
by a process of condensation.
This process is the reverse of evaporating and boiling.
When water vapour that has evaporated from the sea
rises high in the air, it cools and condenses on dust
particles to form tiny water droplets.
Huge numbers of these form clouds and when they join
together they form raindrops.
22. Condensation
(Particletheory)
The particles in a gas possess a large amount of energy,
which they use to move.
If the particles are cooled, they lose some of their
energy and slow down.
If the gas is cooled sufficiently, the particles lose so
much energy that they can no longer bounce off each
other when they meet.
The particles now slide over each other and form a
liquid.
23. Sublimation
A few substances can change from a solid to a gas, or
from a gas to a solid, without forming a liquid.
This process is called sublimation.
Solid carbon dioxide, known as dry ice, sublimes when
it is heated to -78°C.
It can be used on stage to produce a mist in the air
when it warms up, at rock concerts, for example.
Sulfur is released as a gas by volcanoes.
When it cools it sublimes to form solid sulfur around
the volcano's opening or vent.
This solid sulfur is sometimes called flowers of sulfur.
25. Dissolving
When something dissolves in a liquid it forms a
solution.
The liquid is called a solvent and the solid that
dissolves in it is called the solute.
The particle theory explains how things dissolve in the
following way.
There are small gaps between the particles in a liquid.
When a substance dissolves in a liquid, its particles
spread out and fill the gaps.
Particles in a solid solute are pulled apart by the
particles in the liquid solvent, which then move
between them.
