The particle theory, states of matter properties, changes in state of matter, gas pressure, diffusion and atmospheric pressure

1. The particle theory
Chapter 8
(Chemistry)

2. The
particle
theory of
matter
• The particle theory states that matter is made
from particles.
• The particles are s 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 made from atoms and
molecules.

3. The properties of
matter and the particle
theory
There are 3 states of matter and each one has its own special
properties

4.  Strong attraction forces
hold the particles together
in a 3 dimensional
structure .
 The orderly arrangement
is called lattice.
 Particles can move a little
(do not change position),
they vibrate.
Solids
Particles in a solid Properties of solids
 Solids have a definite
mass.
 They have a definite
volume.
 They are hard to
compress.
 They do not flow.

5.  Forces that hold the
particles together are
weaker than solids.
 Particles in a liquid can
change position by
moving around each
other.
Liquids
Particles in a liquid Properties of liquids
 Liquids have a definite
mass.
 They have a definite
volume.
 They are hard to
compress.
 They flow.
 They take the shape of
the container.

6.  Forces that hold the
particles together are very
small.
 Particles can move away
from each other and travel
in all directions.
 When they hit each other
or the walls of the
container they bounce and
change direction
Gases
Particles in a gas Properties of gases
 Gases have indefinite
mass.
 They have indefinite
volume.
 They are easy to
compress.
 They flow and spread.
 They take the shape of
the container.

8. When states of matter
change.
This type of change is a physical change and is reversible.
Melting, freezing, evaporating, boiling, condensing and
sublimation are all examples.

9. Melting
(solid changing into
a liquid)
When solid is heated to its melting point it
loses shape and starts to flow.
The heat energy supplied makes the particles
vibrate more strongly so they push each other
away.
This weakens the forces of attraction between
the particles and allows them to move around
each other.

10. Freezing
(Liquid changing into
a solid)
When liquid is cooled to its freezing point the
particles lose energy and can no longer move
around each other.
The particles vibrate in one position in a
lattice.

11. Evaporation
(liquid changing into
a gas)
A liquid can change into gas over a range of
temperatures without boiling.
Some of the liquid at the surface changes into
gas and mixes with the air as it has more
energy than the rest of the particles in the
liquid.

12. Boiling
When the liquid reaches its boiling point
bubbles of gas form in it which rise to the
surface and burst into the air.
If the boiling liquid is heated strongly, its
temperature does not rise, it just boils quickly.

13. Condensing
(gas changes into
liquid)
When a gas is cooled it condenses to form a
liquid.
The particles in the gas lose some of the
energy which allows them to move so quickly
and they slow down so much that they cannot
bounce off each other.They stay close to each
other and form a liquid.

14. Sublimation
(solid changes into
gas or gas into
solid)
Few substances can change from solid to gas
or from gas to solid without forming a liquid.
The forces are quickly lost or formed when the
particles quickly gain or lose energy.

15. Dissolving
(solid dissolves in a
liquid)
When a solid dissolves in a liquid it seems to
disappear into it.
If it is a coloured substance it may colour the
liquid.
It does not disappear, the particles separate
and spread through the liquid.
This is possible because the liquid has gaps
between its particles, so the particles of the
dissolving substances pass into them.

16. Gas pressure
Solids can generate pressure, example: a
brick on your toes.
Liquids and gases can generate pressure too.
Example:The dam
 You can see from the diagram that the dam is much thicker at
the bottom than it is at the top.This is because the pressure
of the water is much greater deeper down and the dam needs
to be thick at the bottom so that it is strong enough to
withstand this larger pressure

17. If there is a hole in the container’s
surface then liquid will flow
out, at greater depths.... force &
pressure are greater.... escaping liquid is
greater

19. Atmospheric
pressure
 The atmosphere is a mixture of gases that
covers the surface of the earth (1000 km
thick).
It pushes on every cm² of earth’s surface.
The unit of atmospheric pressure is N/cm²
Atmospheric pressure at sea level is called the
standard pressure (1o N/cm²)
This is the pressure at which the boiling point
of any substance is measured

20. Boiling and
low pressure
 If a flask containing a liquid is connected to a
vacuum pump and some of the air above the
liquid is sucked out, there is less air inside the
flask to push on the surface of the liquid
(smaller air pressure).
 The reduced air pressure allows evaporation
to take place more quickly (less heat needed),
so the boiling point is lowered.

21. Boiling and
high pressure
 When a gas gets hot it expands and increases
its pressure on the surfaces around it.
 If water is boiled in a pan with a lid, the steam
escaping from the water pushes on the lid and
makes it rise (allowing the gas to escape).

22. Diffusion
(Processin which one
substance spreads out
through another)