📄 elements and compounds.htm
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<TITLE>Elements, Compounds, and Mixtures</TITLE>
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<P align="center"><FONT size="5"><B>Elements and Compounds</B></FONT></P>
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<P align="center"><A name="element"><B><I>Elements</I></B></A></P>
<P>Any substance that contains only one kind of an atom is known as an <B>element</B>.
Because atoms cannot be created or destroyed in a chemical reaction, elements
such as phosphorus (P<SUB>4</SUB>) or sulfur (S<SUB>8</SUB>) cannot be broken
down into simpler substances by these reactions.</P>
<P>Example: Water decomposes into a mixture of hydrogen and oxygen when an electric
current is passed through the liquid. Hydrogen and oxygen, on the other hand,
cannot be decomposed into simpler substances. They are therefore the
elementary, or simplest, chemical substances - elements.
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<P>Each element is represented by a unique symbol. The notation for each element
can be found on the periodic table of elements.
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<P>The elements can be divided into three categories that have characteristic
properties: metals, nonmetals, and semimetals. Most elements are metals, which
are found on the left and toward the bottom of the periodic table. A handful of
nonmetals are clustered in the upper right corner of the periodic table. The
semimetals can be found along the dividing line between the metals and the
nonmetals.
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<P align="center"><A name="compd"><B><I>Compounds</I></B></A></P>
<P>Elements combine to form chemical compounds that are often divided into two
categories.
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<P>Metals often react with nonmetals to form <B>ionic compounds</B>. These
compounds are composed of positive and negative ions formed by adding or
subtracting electrons from neutral atoms and molecules.
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<P>Nonmetals combine with each other to form <B>covalent compounds</B>, which exist
as neutral molecules.</P>
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