Atomic theory

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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 appropriate theory for plasmas or neutron stars where unusual environments such as extremes of temperature or density prevent atoms from forming.

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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.

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Historical precursors

Template:Main From the 6th century BC, Hindu, Buddhist and Jaina philosophers in ancient India developed the earliest atomic theories. The first philosopher who formulated ideas about the atom in a systematic manner was Kanada who lived in the 6th century BC. Another Indian philosopher, Pakudha Katyayana who also lived in the 6th century BC and was a contemporary of Gautama Buddha, had also propounded ideas about the atomic constitution of the material world. Indian atomists believed that an atom could be one of upto six elements, with each element having upto 24 properties. They developed detailed theories of how atoms could combine, react, vibrate, move, and perform other actions, and had particularly elaborate theories of how atoms combine, which explains how atoms first combine in pairs, and then group into trios of pairs, which are the smallest visible units of matter. This parallels with the structure of modern atomic theory, in which pairs or triplets of supposedly fundamental quarks combine to create most typical forms of matter. They had also suggested the possibility of splitting an atom.

The existence of atoms was also proposed in the 5th century BC 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 Greek 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 was thus largely absent in Europe until the end of the Middle Ages.

During the Middle Ages (the Islamic Golden Age), Islamic scholars developed atomic theories from a synthesis of Greek and Indian atomism. Older Greek and Indian ideas were further developed by Islamic atomists, along with new Islamic ideas, such as the possibility of there being particles smaller than an atom. As Islamic influence began spreading through Europe, the ideas of Islamic atomism, along with the older ideas of Greek and Indian atomism, spread throughout Europe by the end of the Middle Ages, where modern atomic theories began taking shape.

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Development of atomic theory

A modern atomic theory was developed by Rudjer Boscovich in the 18th century, and after that applied in chemistry by John Dalton. Boscovich based his theory mostly on classical mechanics (Newtonian 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.

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Dalton's Atomic Theory

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See also

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Related lists

fr:Théorie atomique ko:원자론 he:התורה האטומית nn:Atomteori zh:原子論

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