atom: Contemporary Studies of the Atom

With many of the problems of individual atomic structure and behavior now solved, attention has turned to both smaller and larger scales. On a smaller scale the atomic nucleus is being studied in order to determine the details of its structure and to develop sources of energy from nuclear fission and fusion (see nuclear energy), for the atom is not at all indivisible, as the ancient philosophers thought, but can undergo a number of possible changes. On a larger scale new discoveries about the behavior of large groups of atoms have been made (see solid-state physics). The question of the basic nature of matter has been carried beyond the atom and now centers on the nature of and relations between the hundreds of elementary particles that have been discovered in addition to the proton, neutron, and electron. Some of these particles have been used to make new types of exotic “atoms” such as positronium (see antiparticle) and muonium (see muon).

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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