Transcript Chapter Four - Mrs. Lee's 8th Grade Science Page

A Matter of Fact
Mixtures, Elements and
Compounds
Adapted from: education.jlab.org/jsat/.../elements_compounds_mixtures.ppt
Mixtures, elements, compounds
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Scientists like to classify things.
One way that scientists classify matter is
by its composition or structure.
Ultimately, all matter can be classified as
mixtures, elements and compounds.
Why isn’t it a good idea to
classify matter by its phases?
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Because one kind of substance can exist in more
than one phase – such as H20. And matter
changes phases rather easily.
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Scientists ask themselves these
questions?
 Is the matter uniform throughout?
 Can it be separated by physical
means?
 Can it be separated by chemical
means?
By asking these questions scientists can
classify matter into three categories:
Mixtures, Elements, or Compounds.
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Mixtures – two or more substances that are not
chemically combined with each other and can be
separated by physical means.
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The substances in a mixture retain their
individual properties.
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Mixtures are either heterogeneous or
homogeneous
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Heterogeneous mixtures are not even throughout
like salad, pizza, or Ocean water.
Homogenous mixtures are even throughout like
milk, blood, or Gatorade
 All homogenous mixtures are solutions
because a substance (a solute) dissolves in
another (a solvent) creating the homogenous
solution.
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Elements – simplest form of pure
substance. They are made of only one
type of atom and they cannot be broken
into anything else by physical or chemical
means.
If it is on the Periodic Table then it is an
element.
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Compounds – pure substances that are
made of two or more elements that have
combined during a chemical reaction.
Compounds can be broken into simpler
substances only by chemical means.
Examples of compounds are water,
hydrogen peroxide, and salt
You can determine what a
substance is by asking questions
and using a flow chart method.
Pure Substance
Mixture
Heterogeneous
Homogonous
Element
Compound