atom: Early Atomic Theory

The atomic theory, which holds that matter is composed of tiny, indivisible particles in constant motion, was proposed in the 5th cent. b.c. by the Greek philosophers Leucippus and Democritus and was adopted by the Roman Lucretius. However, Aristotle did not accept the theory, and it was ignored for many centuries. Interest in the atomic theory was revived during the 18th cent. following work on the nature and behavior of gases (see gas laws).

Sections in this article:

• Introduction
• Contemporary Studies of the Atom
• Discovery of the Atom's Structure
• From Dalton to the Periodic Table
• Early Atomic Theory
• Atomic Weight and Number
• The Electrons
• The Nucleus
• Structure of the Atom
• Bibliography

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