Atomic theory: Encyclopedia - Atomic theory

Atomic theory

In physics, atomic theory is a theory of the nature of matter. It states that all matter is composed of atoms. The philosophical background of the atomic theory is called atomism. The theory applies to the common phases of matter, namely solids, liquids and gasses, as directly experienced on Earth. Strictly speaking, it is not the approriate theory for plasmas or neutron stars where unusual environments such as extremes of temperature or density prevent atoms from forming.

Atomic theory - Importance

Arguably, the atomic theory is one of the most important theories in the history of science, with wide-ranging implications for both pure and applied science. The theory is largely credited to John Dalton, an 18th- and 19th century British chemist.

Modern chemistry (and biochemistry) is based upon the theory that all matter is made up of atoms of different elements, which cannot be transmuted by chemical means. In turn, chemistry has allowed for the development of the pharmaceutical industry, the petrochemical industry, and many others.

Much of thermodynamics is understandable in terms of kinetic theory, whereby gases are considered to be made up of either atoms or molecules, behaving in accordance with Newton's laws of motion. This was, in turn, a large driving force behind the industrial revolution.

Indeed, many macroscopic properties of matter are best understood in terms of atoms. Other examples include friction, material science and semiconductor theory. The latter is particularly important, as it is the foundation of electronics.

Atomic theory - History

The existence of atoms was proposed as early as in the 5th century BCE by the Greek philosophers Leucippus and his pupil Democritus, for which they were called atomists. They argued that all observed phenomena can be in principle explained by the motion of unchanging particles called atoms. Atomism was taken as the basis for a rational world philosophy by the Epicureans. The greatest extant treatise on atomic theory and its implications for religion, human life, the existence of the soul, and death, is De Rerum Natura ("On the Nature of Things"), written in the 1st century BC by Lucretius Carus.

Since Lucretius' work contradicted Christian concepts of an immortal soul (if the soul is composed of atoms, it must perforce perish upon death; therefore there is no afterlife), it was actively suppressed by Christian writers. The concept thus disappeared until it was revived by Rudjer Boscovich in the 18th century, and after that applied in chemistry by John Dalton. Boscovich based his theory on classical mechanics and published it in 1758. The theory was further developed by Amedeo Avogadro and the developers of the kinetic theory of gases such as James Clerk Maxwell and Ludwig Boltzmann.

In the late 19th century, a movement led by Ernst Mach, Wilhelm Ostwald, and Karl Pearson rejected the atomic theory on epistemological grounds. The dispute was not finally settled until Jean Perrin's experimental investigation of Einstein's mathematical theory of Brownian motion in the early 20th century.

Although Dalton was the founder of modern atomic theory, the evolution of atomic theory did not stop there. Ernest Rutherford was a major contributor to the atomic model because he proved that although Dalton and Thompson were partially correct there was still a flaw in both of their models of the atom in that the atom consisted mostly of space. In 1911, Rutherford's gold foil experiment established that the mass of the atom is concentrated in its nucleus, disproving the plum pudding model of the atom. Then in 1915, Niels Bohr further advanced atomic theory by developing the Bohr model of the atom, which soon led to the development of the modern quantum atom. Up until 1932, the prevailing atomic theory had provided evidence for the electron orbiting a nucleus with protons, but it wasn't until that year that James Chadwick added the discovery of the neutron to atomic theory. The study of these subatomic particles eventually lead to the current Standard Model of particle physics.

See also

• Atom
• Atomism
• History of thermodynamics
• Kinetic theory
• Development of Quantum Theory

Atomic theory - Related lists

• Timeline of chemical element discovery
• Timeline of quantum mechanics, molecular physics, atomic physics, nuclear physics, and particle physics
• Timeline of thermodynamics, statistical mechanics, and random processes

Categories: Atomic physics | Statistical mechanics | Chemistry theories | Foundational quantum physics

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