Year 7 Science Revision particles summary sheet updated

Particles Summary Sheet
Mixtures
A mixture is made from different substances that are not chemically joined.
For example powdered iron and powdered sulphur mixed together makes a mixture of iron and sulphur. They can be
separated from each other without a chemical reaction, in the way that different coloured sweets can be picked
out from a mixed packet and put into separate piles.
Separating mixtures
The different substances in mixtures are usually easily separated from one another. The method you use depends
upon the type of mixture you have.
Chromatography
This is good for separating dissolved substances that have different colours, such as inks and plant dyes. It works
because some of the coloured substances dissolve in the liquid better than others, so they travel further up the
paper.
Filtration
Filtration is good for separating an insoluble solid from a liquid. (An insoluble substance is one that does not
dissolve).
Sand, for example, can be separated from a mixture of sand and water using filtration. That's because sand does
not dissolve in water.
Evaporation
This is good for separating a soluble solid from a liquid (a soluble substance does dissolve, to form a solution).
For example copper sulphate crystals can be separated from copper sulphate solution using evaporation. Remember
that it is the water that evaporates away, not the solution.
Simple distillation
This is good for separating a liquid from a solution. For example, water can be separated from salty water by
simple distillation. This method works because the water evaporates from the solution, but is then cooled and
condensed into a separate container. The salt does not evaporate and so it stays behind.
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ParticlesSummary
SummarySheet
Sheet
Particles
The three states of matter
A theory is used to explain observations (data). Scientists also use theories to make predictions,
Expansion and contraction
and test the predictions to find out if they are correct. If the predictions are not correct, then the
theory may have to be changed to explain the new evidence.
Substances expand or get bigger when they are heated up. They contract or get smaller when they are
The different
of solids,
liquids and gases can be explained by the particle theory (or
cooled
down. Thisproperties
property can
be useful.
particle model). Solids, liquids and gases (the three states of matter) need to be handled and
Thermometers
stored differently
work because
because of
thethese
liquiddifferent
inside them
properties.
expands and
For instance,
rises up the
solid
tube
materials
when itcan
gets
be hotter.
taken to
Metal
partssite.
can be fitted together without welding using shrink fitting. The animation shows how this
a landfill
works.
SOLID
Materials expanding and contracting can also cause•problems.
example,
expand
in the
summer
Solids areFor
made
up ofbridges
particles
that are
very
close
heat and need special joints to stop them bending outtogether
of shape.and are held tightly together by strong
What do the particles do
bonds.
• Solids cannot be squashed, do not flow, have
fixed
volume,
and space
are dense
(are heavy
When substances expand or contract, their particles astay
theshape
sameand
size.
It is the
between
the
for
their
size).
(Volume
is
the
amount
of
space
particles that changes:
•
something takes up. It is measured in units such as
3).)
cubicmore
centimetres
The particles in a solid vibrate
when it is(cm
heated,
and take up more room.
•
The particles in a liquid move around each other more when it is heated, and take
up more room.
•
LIQUID
• Liquids
are made
up directions
of particles
thatitare
fairly and
The particles in a gas move
more quickly
in all
when
is heated,
close together; the bonds between the particles are
take up more room.
weaker than the bonds in solids. This allows the
particles to move past each other.
•
Liquids cannot be squashed, flow quite easily and have a
fixed volume but no fixed shape.
•
Although they are dense, liquids are usually less dense
than solids.
GAS
• Gases are made up of particles that are well
spread out, with no bonds between them.
• Gases are quite easy to squash, flow easily, have no
fixed volume and no fixed shape.
The particles in a solid vibrate more and take up more room when the solid is heated
•
Gases are not dense.
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Particles Summary Sheet
The three states of matter
A theory is used to explain observations (data). Scientists also use theories to make predictions,
and test the predictions to find out if they are correct. If the predictions are not correct, then the
theory may have to be changed to explain the new evidence.
The different properties of solids, liquids and gases can be explained by the particle theory (or
particle model). Solids, liquids and gases (the three states of matter) need to be handled and
stored differently because of these different properties. For instance, solid materials can be taken to
a landfill site.
SOLID
• Solids are made up of particles that are very close
together and are held tightly together by strong
bonds.
• Solids cannot be squashed, do not flow, have
a fixed shape and volume, and are dense (are heavy
for their size). (Volume is the amount of space
something takes up. It is measured in units such as
cubic centimetres (cm3).)
LIQUID
• Liquids are made up of particles that are fairly
close together; the bonds between the particles are
weaker than the bonds in solids. This allows the
particles to move past each other.
•
Liquids cannot be squashed, flow quite easily and have a
fixed volume but no fixed shape.
•
Although they are dense, liquids are usually less dense
than solids.
GAS
• Gases are made up of particles that are well
spread out, with no bonds between them.
• Gases are quite easy to squash, flow easily, have no
fixed volume and no fixed shape.
•
Gases are not dense.
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Particles Summary
(
i
d)
Diffusion
The natural mixing of substances is called diffusion. Diffusion occurs because particles in a
substance are always moving around. Diffusion is fastest in gases, and slower in liquids.
Dilution
When you add water to orange squash you dilute it. The colour becomes paler because the orange
coloured squash particles are spread out more by the water particles.
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Pressure in gases
Pressure is caused by particles hitting the walls of the container they are in. The pressure may
increase because:
• the container has been squashed, making the volume smaller; this means that the particles will
be hitting the walls more often.
• the number of particles has been increased, which means there are more particles moving around
to hit the walls.
• the temperature of the particles has increased, so they will move around faster and hit the walls
harder and more often.
If the particles are in a flexible container, like a balloon, an increase in pressure will make the
volume increase. If the pressure becomes too great the balloon will burst.
Air pressure is the pressure caused by air particles around us. Air pressure lets us suck things up
using a straw and also causes a container to collapse if the air is sucked out. If all the air is sucked out
of a container, you get a vacuum – nothingness.