matter: Modern Theory of Matter

The modern theory of matter dates from the work of John Dalton at the beginning of the 19th cent. The atom is considered the basic unit of any element, and atoms may combine chemically to form molecules, the molecule being the smallest unit of any substance that possesses the properties of that substance. An element in modern theory is any substance all of whose atoms are the same (i.e., have the same atomic number), while a compound is composed of different types of atoms together in molecules.

Sections in this article:

• Introduction
• The Relationship of Matter and Energy
• Physical and Chemical Changes
• Modern Theory of Matter
• Early Theories of Matter
• The States of Matter
• The Properties of Matter
• Bibliography

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2024, Columbia University Press. All rights reserved.

See more Encyclopedia articles on: Physics