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A compound is a pure substance
composed of two or more different atoms chemically bonded to one another.
A compound can be destroyed by chemical means. It might be broken down into simpler
compounds, into its elements or a combination of the two, whereas the same techniques
do not cause an element to break down.  | Microscopic
view of the molecules of the compound water (liquid phase). Oxygen
atoms are red and hydrogen atoms are white. |
A
compound consists of atoms of two or more different elements bound together,
can be broken down into a simpler type of matter (elements) by chemical means
(but not by physical means), has properties that are different from its component
elements, and always contains the same ratio of its component atoms. A
molecule consists of two or more atoms of the same element, or different
elements, that are chemically bound together. A molecule is the smallest particle
in a chemical element or compound that has the chemical properties of that
element or compound. Molecules are made up of atoms that are held together by
chemical bonds.
EXAMPLES
OF IONIC AND COVALENT COMPOUNDS:
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Ionic Compound--
Ionic compounds
are defined as being compounds where two or more ions are held next to each other
by electrical attraction. The formation of an Ionic bond is the result of the
transfer of one or more electrons from a metal onto a non-metal. The result is
that one of the ions will have a positive charge (called a "cation") and the other
will have a negative charge ("anion"). Cations are usually metal atoms and anions
are either nonmetals or polyatomic ions (ions with more than one atom). All ionic
compounds form crystals. Ionic
compounds have a definite melting point and contain ionic bonds.When dissolved
in water they will conduct electricity. An example would be sodium
chloride (NaCl). To view the 3-D structure of a salt crystal click
here.
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Covalent
Compound-- A covalent compound is a compound in which the atoms
that are bonded share electrons rather than transfer electrons from one to the
other. While ionic compounds are usually formed when metals bond to nonmetals,
covalent compounds are formed when two nonmetals bond to each other. The
water molecule shown to the left is composed of two different types of atoms covalently
bound: oxygen (red) and hydrogen (white). To
view the 3-D structure of water click here.
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Compound-- The aspirin molecule shown to the left is composed of
three different types of atoms: carbon (green), oxygen (red) and hydrogen (white)
covalently bound. To
view the 3-D structure of aspirin click here.
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