Pure substances are subdivided into two categories: elements
An element is a substance that
cannot be separated into simpler substances by chemical reactions. In the periodic
table, there are over 100 of these elements. Most of them can be found naturally
on Earth. Others are produced synthetically by nuclear reactions.
Elements are indicated by symbols. It is important to note that
the symbol for an element is case-sensitive. The convention is:
the first letter of the symbol of an element is always capitalized
the second and third letters are never capitalized.
to view the Periodic Table of elements. See pictures of them and how they are found and used. For most elements the symbol is the abbreviated form of
its English name, using one or two letters.