Pure Substances vs. Mixtures
Physical and Chemical Changes
Everything that has mass and
takes up space is called matter.
There are 2 types of matter:
• Pure Substances
• Mixtures
There are two kinds of pure
substances
Elements
Compounds
Matter that has a fixed composition
and definite properties. (chemical and
physical)
Elements
• Substance that cannot be separated or
broken down into simpler substances by
chemical means.
• Ex’s- any box on the periodic table
• Made of only 1 type of atom
– The smallest unit of an element that
maintains the properties of that element
• HUH?
The smallest unit of an element that
maintains the properties of that element???
• The element sodium has certain properties
– 11 protons, 11 electrons…boiling point, etc
Compounds cont…
• Substance made of atoms of 2 or more different
elements that are CHEMICALLY combined.
• Elements are combined in a definite way and this
changes their properties
Na- lethal if ingested Cl- lethal if ingested
NaCl- table salt
Molecules
• Two or more atoms bonded together…
– Ex- O2, NaCl, etc.
– Not all molecules are compounds, but all compounds
are molecules…explain
Compounds
• Molecules made by
two or more elements
bonded together always in a definite
ratio
NaCl
(sodium
chloride/salt)
Elements
• Molecules made of
just one element
Na
(sodium)
• Cannot be separated into simpler substances
by physical methods (physical changes)
• Fixed composition
– Properties do not vary
• Can be expressed with a chemical formula
– Ex H2O, NaCl, H
•Mixtures are two or
more substances that are
physically combined.
•(NOT chemically
combined like a pure
substance)
•May be separated into
pure substances by
physical methods
Examples of Mixtures
• Components retain their characteristic
properties and can be separated by physical
means.
• http://videos.howstuffworks.com/hsw/22540-together-but-separatesuspensions-video.htm
This sand and iron filings
mixture can be separated
using a magnet.
Two types of mixtures
•Homogenous mixtures look the same throughout
•Types: solutions, alloys, etc.
•Example: salt water, brass
• Have the same composition
throughout
• Components are indistinguishable
• Will not scatter light
• Particle size is small
Can they still be separated by
physical means ?
YES!!! It may be more
complicated, but it can be
done…distillation ,
centrifugation
•Solutions are …
•homogenous mixtures that do not scatter light.
•separated by physical means (including
distillation or evaporation.)
•created when something is completely dissolved
in pure water.
Examples: sugar water, salt water
Parts of a Solution
•Solute- substance that dissolves in solvent
ex. Salt (“U dissolve”)
•Solvent- substance that does the dissolving
(ex.water)
Well, not really,
because you
don’t dissolve,
but you get the
picture 
Why don’t you dissolve?
• You are not “Miscible”
– Miscible- two or more liquids that can dissolve
into each other
– Immiscible- liquids that do NOT mix
• Ex- oil and water
Heterogeneous mixtures are composed of
large pieces that are easily separated by
physical means (ie. density, polarity,
metallic properties).
• Do not have same composition throughout
• Components are distinguishable
• Particle size is medium or large
Examples: fruit salad, vegetable soup, etc.
Tyndall Effect
• Scattering of light due to particles
1.
Colloid –medium particles
• Particles stay suspended in the
mixture and scatter light (Tyndall
effect)
• Ex- mayonnaise, milk, fog
1.
Suspension- large particles
• Tyndall effect
• Particles will settle out when the
mixture is allowed to stand
• Ex-muddy water, OJ with pulp
• Physical properties are those that we can
determine without changing the identity of
the substance we are studying.
• Properties we can observe or measure
– Ex- color, state of matter, etc
DENSITY
Mass per unit volume
Calculated by:
Density= Mass/Volume
D=M/V
• Hardness, color, melting point
and density are all physical
properties.
• The physical properties of
sodium (NaCl) metal
–
–
–
–
soft, lustrous
silver-colored metal
relatively low melting point
low density.
Chemical and
Physical
Properties
Physical Properties
• Physical properties can be determined
without changing the identity of the
substance.
• Examples???
Viscosity
• Resistance to flowing
Maple Syrup- High Viscosity
Water- Low Viscosity
Ductility
• Ability to be drawn into a thin wire
Malleability
• Ability to be hammered into thin sheets
without shattering
Hardness
• A substance’s resistance to being scratched
Solubility
• Ability to dissolve in water
– Yes! It is a physical property
because you do not need to alter
identity of the substance to
determine solubility.
Conductivity
• Ability to carry electricity
High Conductivity (the liquid is
able to let electrons flow to
complete the circuit
Low Conductivity (the liquid is
NOT able to let electrons flow to
complete the circuit
What is a superconductor?
• Watch this video and try to write a one
sentence definition.
Video on Superconductors
Other examples of physical
properties….
Chemical Properties
• Describe the way a substance can
change or react to form other
substances.
– (NOT the actual reaction- that’s a
chemical __________)
• Must be determined using a process
that changes the identity of the
substance
• One of the chemical properties of alkali metals
such as sodium and potassium is that they react
with water. To determine this, we would have to
combine an alkali metal with water and observe
what happens.
• In other words, we have to define chemical
properties of a substance by the chemical changes
it undergoes.
Ex’s of Chemical Properties
• Reactivity: ability of a substance to
combine CHEMICALLY (at the electrons)
with another substance (to form a
compound)
Flammability
• Ability of a material to burn in the presence
of Oxygen.
Alkalinity
• Ability to neutralize acids
•A change that does not change the chemical
composition of a substance.
•Ex: changes in size, shape, appearance, etc.
Why? The form or appearance has changed, but
the properties of that substance are the same (i.e. it
has the same melting point, boiling point, chemical
composition, etc.)
• PHYSICAL CHANGE:
• Changes in Temperature
– Melting, Boiling, Freezing
•
•
•
•
•
Changes in Color
Conducting electricity
Dissolving
Hammering into a sheet
Drawing into a wire
• PHYSICAL PROPERTY
• Melting Point, Boiling
Point, Freezing Point
• Color
• Conductivity
• Solubility
• Malleability
• Ductility
•A chemical change occurs when a substance
changes into something new.
•This occurs due to heating, chemical reaction,
etc.
•You can tell a chemical change has occurred if
the density, melting point or freezing point of
the original substance changes. Many common
signs of a chemical change can be seen (bubbles
forming, mass changed, etc).
•Recall: A chemical change occurs when a
substance changes into something new.
•Foaming
•Bubbles
•New odor
•Heat production or drop in temperature
•New precipitate (solid formed from liquids)
– You can’t go
back to the
original
substances
after a
chemical
change
(reaction) has
occurred!!
Baking
soda
reacting
w/
vinegar
Burning
wood
There is no observable change in the
quantity of matter during a chemical
reaction or a physical change.
In other words, matter cannot be created
nor destroyed. It is just converted from
one form to another
Answers to bottom of notes…
1. Photosynthesis
1. Chemical Change
2. Burning charcoal
2. Chemical Change
3. Breaks easily
3. Physical Property
4. Fizzes with vinegar 4. Chemical Property
5. Tea kettle boiling
5. Physical Change
6. Digestion of food
6. Chemical Change
7. Painting a house
7. Physical Change
8. Grinding meat into 8. Physical Change
hamburger
9. Reacts with air
9. Chemical Property
10.Has a sour odor
10.Physical Property
Property
Description
Hardness
Ability of 1 substance Diamond can scratch
to scratch another
glass
Viscosity
Resistance to
flowing
Solubility
Example
Water= low visc.
Honey= high visc.
Ability to dissolve NaCl dissolves
in water
easily in water so
it’s soluble
Property
Description
Example
Superconductor
Substance that
conducts electricity at
lower temperatures
Substance that has a
resistance b/w a
conductor & insulator
Tin,
aluminum,
used in trains
Silicon-used
in computers
or radios
Semiconductor