Atomic theory

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The 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. This definition is valid for the matter commonly surrounding us. Strictly speaking, it is not valid in plasmas or other particular environments, characterized for instance by very large pressure (e.g. neutron stars).


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.


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.

Lucretius' work exposed problems with the 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.

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