Grade 7 Science
Unit 3:
Mixtures & Solutions:
The Particle Theory
Particle Theory of Matter
 All
matter is made up of
tiny particles.
 These particles are always
moving… they have
energy.
 There
are spaces among
particles.
 There are attractive forces
between the particles.
 The particles of one
substance differ from the
particles of other
substances.
Student Activity...
With a partner decide:
1. How would you tell the
difference between a pure
substance and a mixture?
2. How would use the
Particle Theory of Matter
to support your answer to
question #1?
Mixtures vs. Pure
Substances
Mixtures...
 MAY
have distinct visible
components.
 MAY appear uniform
throughout.
 They
are the physical
combination of two or
more pure substances.
+
Sugar
=
Water
?
Examples of Mixtures…
•salt water, kool-aid
•chocolate chip cookie
•muddy water
•salad dressing
•air
Pure Substances...
 ALWAYS
appear as
uniform throughout
 They contain either a
single atom or two or more
atoms chemically
combined to form a
different substance.
Examples of Pure Substances
•sugar (C12H22O11)
•gold (Au), copper (Cu)
•distilled water (H2O)
•carbon dioxide (CO2)
•oxygen (O2)
Student Activity...
Read pages 232, 236 and 237
Make a list of 15-20 solutions
and mixtures that you
encounter in a day. * those
that may pose a safety risk.
Grade 7 Science
Homogeneous &
Heterogeneous
Mixtures
Homogeneous Mixture
 also
called
solutions
 can be
solid, liquid
or gas
Stainless steel
 the
particles
are evenly
mixed so
that none of
the original
substances
are visible
Kool-aid
 they
appear
to be ONE
substance
 light passes
through
unaffected
Heterogeneous Mixtures
 also
Granola bar
called
mechanical
mixtures
 can be
solid, liquid
or gas
 the
Concrete
different
parts are visible
to the eye (may
need a
microscope)
 the particles do
 Light
will
reflect
perpendicula
r to the
direction of
the beam
Student Activity...
 Create
a chart and list the
various homogeneous and
heterogeneous mixtures in
your home.
 Share with your shoulder
partner and add to your
The Tyndall Effect
A
phenomenon that can be
used to distinguish between
solutions and what appears
to be a solution
 cannot be used to distinguish
between a solution and a
pure liquid
In a Solution...
 Light
passes
unaffected (if a
student looks at the
beaker perpendicular
to the direction of the
beam they will NOT
see it
In a Mechanical Mixture...
 The
light will
scatter as it
passes through
the mixture
because all
particles are not
Both Hetero and
Homogenoeus Mixtures?
Complete Activity 7-1C
Page 238 & 239
Post Activity Discussion...
Enrichment
Colloids
Dispersions
Emulsions