MATTER AND ENERGY

2.4 - Classification of Matter

2.4.1 - Pure Substances

Pure substances are subdivided into two categories: elements and compounds.

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:

1. the first letter of the symbol of an element is always capitalized
2. the second and third letters are never capitalized.

Click here 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.

Some elements like gold, iron, sodium, potassium, lead, mercury, copper have symbols based on their Latin names.

A compound is a substance that is composed of two or more elements chemically held together in fixed proportions. Do you know what fixed proportion mean?

Section 3.2
Composition and Properties of Matter ..p52

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