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Why are elements and compounds classified as
pure substances?
How do mixtures differ from pure substances?
What is the main difference among solutions,
suspensions, and colloids?
Element:
Gold
Compound:
Dry Ice
Matter can be pure, such as an element (gold), or a compound
(water).
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Elements
Cannot be broken down into simpler substances by ordinary
chemical changes
 Only about 100 known
 An atom is the smallest particle of an element that has the chemical
properties of that element. (An element consists of atoms of only
one type.)
 At room temperature, most elements are solids.

 Al - Aluminum (aluminum foil, soft drink cans)
 C- Carbon (main element in pencil lead)

Some elements are gases at room temp.
 Oxygen and nitrogen

Two elements are liquids at room temperature
 Bromine and mercury (both extremely poisonous)
Turn to page 39 in your textbook. What are some characteristics
of the elements pictured here?
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1813 - Jons Berzelius (Swedish chemist) suggested chemists use symbols
(Class participation points opportunity!!!)
Symbols allow scientists to communicate without confusion (regardless of
language)
A molecule is a group of atoms
that are held together by
covalent bonds so that they move
as a single unit.

A substance made from two or more simpler
substances joined in a fixed proportion (A
substance made up of two or more different types
of atoms bonded together.)
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Water (H2O)
Properties differ from those of the substances
from which the compound is made

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O and H are gases at room temperature, H can fuel
fire, O can keep it burning
Water is a liquid at room temperature but does not
burn or help other substances to burn
Coming Soon!
Matter can be a mixture. Mixtures are a combination of two or more
substances that do not combine chemically but remain the same individual
substances. Mixtures can be separated by physical means. Mixtures contain
two or more pure substances.
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Properties can vary


Composition is not fixed


can retain some properties of their individual substances
but properties are less constant than properties of a
substance
Think of a salad
Heterogeneous and Homogeneous Mixtures
Hetero – parts are noticeably different(sand=light and dark parts)
 Homo – parts are difficult to distinguish(stainless steel=iron,
chromium and nickel)

How can you tell sand is a heterogeneous mixture?
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Solutions – sugar water, windshield wiper fluid
–homogenous mixture
–will not separate over time
Suspensions – sandy water, Italian salad dressing
– heterogeneous mixture
– separates into layers over time
– scatters light

Colloids – fog, homogenized milk
– homogeneous or heterogeneous depending on approach
– water, sugar, proteins, fats
– do not separate into layers
– scatters light
*What happens to suspended particles over time?
*How does a mask prevent a worker from
inhaling particles of plastic suspended in the air
after they’ve been sanded from a surfboard ?
*Consider creating a three part Venn diagram on mixtures.
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Solutions
A solution is a homogeneous
mixture of two or more
components. The dissolving
agent is the solvent. The
substance which is dissolved
is the solute. The components
of a solution are atoms, ions,
or molecules, which makes
them 10-9 m or smaller in
diameter.
Examples: Sugar dissolved in
water, Salt dissolved in water
Carbon dioxide or oxygen in
water, Water vapor in air, Hexane
in paraffin wax, Mercury in gold
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Suspensions
The particles in suspensions
are larger than those found in
solutions. Components of a
suspension can be evenly
distributed by a mechanical
means, like by shaking the
contents, but the components
will settle out.
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
Example: Oil and water, Fine
sand in water, Paint, Dust in air,
Droplets of oil in air
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Colloids
Particles intermediate in size
between those found in
solutions and suspensions
can be mixed such that they
remain evenly distributed
without settling out. These
particles range in size from
10-8 to 10-6 m in size and are
termed colloidal particles or
colloids. The mixture they
form is called a colloidal
dispersion. A colloidal
dispersion consists of
colloids in a dispersing
medium.
Example: Aerosol (liquid dispersed
in a gas - fog, mist, clouds)
Foam (gas dispersed in a liquid soda (CO2 dissolved in water),
whipped cream)
Solid Foam (gas dispersed in a solid Styrofoam, plaster)
Emulsion (liquid dispersed in a
liquid - butter, milk)
Matter
Anything with mass and volume.
Substance
Matter with constant
composition
Mixture
Matter with variable composition
Element
Substance
made up of
only one
type of
atom
Compound
Two or more
elements that
are chemically
combined
Heterogeneous
Mixture
Mixtures that are
made up of more than
one phase
Homogeneous
Mixtures
Also called solutions.
Mixtures that are
made up of only one
phase
Examples
- gold,
silver,
carbon,
oxygen and
hydrogen
Examples water, carbon
dioxide, sodium
bicarbonate,
carbon
monoxide
Examples - sand,
soil, chicken soup,
pizza, chocolate chip
cookies.
Examples - salt
water, pure air, metal
alloys, seltzer water.
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How are the two brands of mixed nuts alike?
How are they different?
What is the percent by mass of each type of nut
in each can?
Do the contents of each can meet the FDA
regulations? Explain
On the Brand A label, the nuts are listed in this
order: peanuts, Brazil nuts, almonds, cashews,
pecans, and hazelnuts. What do you think
determines the order?
When can physical properties be observed?
What observations might indicate that a physical
change has occurred?
A physical property is any characteristic of a
material (substance) that can be observed or
measured without changing the compositions
(identities) of the substances in the material. (See
pages 45-47.)
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Viscosity
Conductivity
Malleability
Hardness
Melting point
Boiling point
Density
Consider a Layered
Foldable Reflection

To Identify Materials

To Choose Materials

To Separate Mixtures

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Filtration
Distillation
• Physical properties can be observed without
changing the substance.
• Physical changes can change some physical
properties but do not change the substance.

Some of the properties change but substances in
the material remain the same
Water
Liquid
Butter (solid) in a pan

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Gas
(heated)
liquid butter
Crumpling or slicing changes size and shape but
not composition
Some physical changes can be reversed and others
cannot (braids and ice, verses sliced tomatoes or
peeled oranges)
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When can chemical properties be observed?
What observations might indicate that a
chemical change has occurred?
What is the difference between chemical and
physical changes?
Chemical properties have the ability to produce a
change in the composition of matter.

Can only be observed changing into different
substances
Flammability (combustion)
 Reactivity

 rusting(oxidation)
 tarnishing

Change in color

Production of a gas

Forming a precipitate
Comparing and Contrasting
Physical and Chemical Properties
Do you have ideas for how this information could be
organized using a tool a scientist might use?
Physical or
chemical change?
Use a Venn Diagram, Table or T – chart
One Example:
Physical Change
Chemical Change
Composition of matter
remains the same
Composition of matter
changes
Some can be reversed and
some cannot
Can be reversed but it’s not
easy
Another opportunity for class participation credit…
Read
Research
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