Pure Substance - DOC by CbDCunX0


									         What is a Pure Substance?
1   A pure subtance is a form of matter that always has a
    definite and constant composition.

2   Pure substances have a set of unique properties by
    which they can be identified.

Element:            is a pure substance whose basic unit is a
               single atom or homoatomic molecule.
    a)   gold, silver, sodium, carbon, sulfur, oxygen, nitrogen, helium

    b)   There is a limited library of elements or types of atoms (110), of
         which only 88 are found in nature

    c)   Elements cannot be broken down into simpler substances by
         chemical or physical means.

Compound:                 is a pure substance when isolated
                     from other compounds, whose basic unit
                     is a heteroatomic molecule.
    a)   Salt, sugar, water, proteins, alcohol

    b)   Heteroatomic molecules contain at least two different types
         of elements combined in definite ways

    c)   Once elements combine to form a compound, the original
         charateristic properties of the elements are replaced by the
         properties of the compound, which in many cases are very
         different from those of the elements

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