Composition of
Matter
Elements, Compound, &
Mixtures
Chapter 21.4 & 21.5
P 361-363
Pure Substances
• Have you ever looked at a picture
and couldn’t tell whether it was a
painting or copy? Did you go up
and touch it?
• The properties of materials can
be used to classify them into
categories.
Pure Substances
• Materials are either pure substances or a
mixture of substances.
• Pure substances are either an element or
compound
Elements
• Remember:
– An atom is the smallest piece
of matter that still retains the
properties of the element.
• All substances are made
from atoms.
• If all the atoms in a
substance are alike, it is
called an element.
Elements
• The graphite in your pencil is an
example of an element.
– All the atoms in the graphite are carbon
atoms
• The copper covering on a penny is
an example of an element.
– All the atoms that make up the covering
are copper atoms.
• The zinc in the middle of a penny is
an example of an element.
– All the atoms that make up your penny
center are made of the element zinc.
Elements
• There are 90 elements found in nature
• Over 20 have been made in laboratories
– These are usually unstable and don’t last long
•Some elements you might recognize
in your everyday life.
Copper pot or pan
Elements
• How many atoms are bound
together in an element is shown
by an elemental formula.
– Many elements have the basic
unit of one individual atom.
• The elemental formula for these
elements is the chemical symbol
found on the periodic table
• Example: Gold’s elemental formula
is Au
Elements
• Some elements are found in basic
units of two or more.
– Example: Oxygen’s elemental formula
is O2
• The subscript 2 shows that there are two
atoms of oxygen in each molecule of
Oxygen
Compounds
• Two or more elements can combine to
form a compound
• These elements combine in a fixed
proportion
– Example: water is a compound in which 2
hydrogen atoms combine with 1 oxygen
atom
• Can you imagine putting an explosive
silvery metal and a greenish-yellow,
poisonous gas on your food??
Compounds
• You may have if you dashed some
table salt on your food today!
• Salt is a compound made up of
the 2 elements sodium and
chlorine
• Like salt, compounds usually look
different from the elements in
them
Compounds
• A compound is represented by its
chemical formula.
– The chemical formula is made from the
symbols of the elements that make the
compound up.
– Sodium Chloride’s chemical formula is
NaCl
• Na is the symbol for Sodium
• Cl is the symbol for Chlorine
• We will learn how to write these formulas
later.
Mixtures
• Who enjoys eating pizza and pop
for lunch?
• If so, then you enjoy 2 foods that
are classified as mixtures
• A mixture, such as pizza or pop, is
a material made up of two or more
substances that can be easily
separated by physical means.
Mixtures
Heterogeneous Mixtures:
• Unlike compounds, mixtures aren’t
always made of the same proportions
of the substances that make them up.
• Remember that pizza? The chef
doesn’t measure out precisely how
much of each topping is sprinkled on.
Plus, you can easily see most of the
toppings on the pizza
• A mixture in which different materials
can be seen easily is called a
heterogeneous mixture
• Other examples: granite, dry soups,
concrete
Suspensions
• A suspension is a mixture that will
separate if left undisturbed
– The particles can be seen “suspended”
in the suspension
• Example: Sand in water – the sand does not
dissolve in water
– The sand is able to separate from the water
over time.
– The sand can “settle”
– Particles are large
• Light can not be shown through a
suspension
– Suspensions “scatter” light
Mixtures
Homogeneous Mixtures:
• Remember that pop? It’s an example
of a homogeneous mixture
• A homogeneous mixture contains 2
or more substances blended evenly
throughout
• There are three special types of
Mixtures:
– Solutions, Suspensions, and Colloids
Solutions
• Solutions are mixtures that do not
separate if left undisturbed.
– The particles are dissolved into the
liquid.
• Example: Salt Water- when salt is dissolved
in water the water and salt will not separate
if left undisturbed.
• The salt does not “settle”
– The salt is the solute
– The Water is the solvent
• Particles are small
• Light can be shined right through a
solution
– Does not scatter light
Colloids
• A colloid is a type of mixture that
never settles
• Its particles are larger than those in
solutions but not heavy enough to
settle
• Examples: Milk, paint, fog
Colloids
Detecting Colloids:
• To tell for certain if a liquid is a colloid, pass
a beam of light through it
• A light beam is invisible as it passes
through a colloid, but can be seen when
passing through a solution
• This occurs because the particles in a
colloid are large enough to scatter light
• The scattering of light by colloidal particles
is called the Tyndall effect
• Can you think of any other colloids?
Element, Compound, Mixture
Properties of Matter
Section 2
p. 526-533
Physical properties
• Physical properties are
observations that you make without
changing the identity of the
substances that make up the
material
• For instance, you can stretch a
rubber band or bend a piece of wire
• The ability to stretch or bend are
physical properties
• Some other physical properties are
color, shape, size, melting point,
and boiling point
Physical Properties
• Appearance:
• How would you describe a tennis
ball? (shape, color, state of matter)
• How would you describe a soft
drink?
(color, state of matter,
taste)
• You could also measure its volume
and temperature—these are all
physical properties
Physical Properties
• Behavior:
• Some physical properties
describe the behavior of a
substance
• For instance, objects
containing iron (I.e. safety
pins) are attracted by a
magnet
• Remember that soft drink? If
you were to knock it over, it
would spread onto the table
and floor—the ability to flow is
a physical property of liquids
Physical Properties
to Separate
• Have you ever licked the icing from the
middle of a sandwich cookie?
• If so, then you’re using physical
properties to identify the icing and
separate it from the rest of the cookie
• You can use other physical properties to
separate such as using a sifter to
separate poppy seeds from sunflower
seeds
• Or sand from iron fillings by using a
magnet
Physical Change
• If you break a piece of gum, you
change some of its physical
properties—shape and size
• However, you haven’t changed the
identity of the materials that make
up the gum
• Each piece still tastes and chews
the same
Physical Change
• A physical change is any
change in size, shape, or state of
matter
• These changes might involve
energy changes, but the kind of
substance—the identity of the
element or compound—does not
change!
Physical Change
So, does a change in state mean that a new
substance has formed?
Physical Change to Separate
• In some parts of the world, water is
very scarce, many such areas lie
near the sea
• They obtain their drinking water by
using the physical property of boiling
point to separate the the salt from
the water
• This process is called distillation
• In distillation, you use an apparatus
to vaporize and condense liquid,
leaving the solid material behind
Chemical Properties
• Have you ever seen the
warning labels on paint thinners
and lighter fluids that read
“FLAMMABLE”
• Flammability is a chemical
property
• Burning produces new
substances during a chemical
change
Printable Page
• Your Text Here
Transitional Page
Backdrops:
www.animationfactory.com
- These are full sized
backdrops, just scale them up!
- Can be Copy-Pasted out of
Templates for use anywhere!