Page 16 - Encyclopedia of Chemical Compounds 3 Vols

Reader’sGuide

represented by a ball of some size, shape, and/or color. The
chemical bond that holds them together is represented by
sticks. This can be represented on paper in a drawing that
simulates a three-dimensional model, by computer software,
or actually in three dimensions from a kit with balls and
sticks.
All three kinds of structural formulas are given for each
compound described in this book. The only exception is
some very large compounds known as polymers that contain
many hundreds or thousands of atoms. In such cases, the
formulas given shown only one small segment of the
compound.
Compound Type: Millions of chemical compounds exist.
To make the study of these compounds easier, chemists
divide them into a number of categories. Nearly all com-
pounds can be classified as either organic or inorganic.
Organic compounds contain the element carbon; inorganic
compounds do not. A few important exceptions to that rule
exist, as indicated in the description of such compounds.
Both organic and inorganic compounds can be further
divided into more limited categories, sometimes called
families of compounds. Some families of organic compounds
are the hydrocarbons (made of carbon and hydrogen only),
alcohols (containing the -OH group), and carboxylic acids
(containing the -COOH groups). Many interesting and impor-
tant organic compounds belong to the polymer family. Poly-
mers consist of very large molecules in which a single small
unit (called the monomer) is repeated hundreds or thousands
of times over. Some polymers are made from two or, rarely,
three monomers joined to each other in long chains.
Most inorganic compounds can be classified into one of
four major groups. Those groups are the acids (all of which
contain at least one hydrogen (H) atom), bases (which all
have a hydroxide (OH) group), oxides (which all have an
oxygen (O)), and salts (which include almost everything else).
A few organic and inorganic compounds described in this
book do not easily fit into any of these families. They are
classified simply as organic or inorganic.
Molecular Weight: The molecular weight of a compound
is equal to the weight of all the elements of which it is made.
The molecular weight of carbon dioxide (CO 2 ), for example,
is equal to the atomic weight of carbon (12) plus two times

CHEMICAL COMPOUNDS xv