Pure Substances
Mixtures
Physical and Chemical Changes
Everything that has mass and
takes up space is called matter.
Matter that has a fixed composition
and definite properties. (chemical and
physical)
There are two kinds of pure
substances
Elements
Compounds
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.
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
• May or may 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
How does matter change?
All matter, regardless of state,
undergoes physical and
chemical changes. These
changes can be microscopic or
macroscopic.
• Physical properties are those that we can
determine without changing the identity of
the substance we are studying.
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
• The physical properties of sodium (NaCl) metal
can be observed or measured. It is a soft, lustrous,
silver-colored metal with a relatively low melting
point and low density.
• Hardness, color, melting point and density are all
physical properties.
•A physical change occurs when the substance
changes state but does not change its chemical
composition.
•For example: water freezing into ice, cutting a piece
of wood into smaller pieces, etc.
•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.)
• Freezing water (a.k.a. wah! wah!) is a
physical change because it’s still water if
it’s frozen or liquid (it’s the same junk!!)
ICE ICE BABY!!
•
•
•
•
•
Melting point
Boiling point
Vapor pressure
Color
State of matter
•
•
•
•
Density
Electrical conductivity
Solubility
Adsorption to a
surface
• Hardness
• Chemical properties describe the way a
substance can change or react to form other
substances.
• These properties, then, must be determined
using a process that changes the identity of
the substance of interest.
• 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.
•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).
– 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