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Elements, Compounds, & Mixtures:

Objectives:

    1.    Explain the difference between an element and a compound.

    2.    Compare heterogeneous and homogeneous mixtures.

    3.    Describe several techniques to separate mixtures.

Key Terms:

    element    compound    pure substance    mixture    heterogeneous mixture    homogeneous mixture

Web Resources:

 

Notes:

Matter can be better defined by separating it into its simplest parts.  Since the atom is the basic unit of matter, we will start there.  A group of similar atoms is called an element.  Here are some elemental facts.
An element cannot be separated into simpler substances by physical or chemical means.
There are slightly more than 100 known elements. (listed on the periodic table)
The periodic table organizes elements by their properties.
Can be represented by a one or two letter abbreviation. (C,H,O,N,P,Na,Cl,Al,Ca)

Aggregates (combinations) of elements can form compounds.  Its important to know that compounds are pure substances.  (A compound of H2O contains nothing but H2O.)  Here are some facts regarding compounds.
Compounds form during chemical reactions. (2H2 + O2 = 2H2O)
Compounds can be separated into their elements by chemical means. (2H2O =  2H2 + O2)
The symbols used to describe compounds describe the exact amount of atoms on the compound. (C6H12O6)
Cannot be separated by physical means.

Aggregates of substances (compounds, elements, or mixtures) combine to form mixtures.  Mixtures can either appear homogeneous (do not contain visibly different parts - milk) or heterogeneous (visibly different parts - chocolate chip cookie)  Here are some facts regarding mixtures.

Must be able to separate into two or more pure substances.
Can be separated by physical means. (do not cause a physical change)
    filtration
    distillation (boiling)
    crystallization (evaporation)
    chromatography (flowing along a stationary surface)
    centrifugation (spinning to find differences in weight)
 

 

Last modified: September 12, 2002