atomic theory

noun
1.
Physics, Chemistry. any of several theories describing the structure, behavior, and other properties of the atom and its component parts.
2.
Philosophy, atomism ( def 1 ).

Origin:
1840–50

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World English Dictionary
atomic theory
 
n
1.  any theory in which matter is regarded as consisting of atoms, esp that proposed by John Dalton postulating that elements are composed of atoms that can combine in definite proportions to form compounds
2.  See atomic structure the current concept of the atom as an entity with a definite structure

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Encyclopedia Britannica
Encyclopedia

atomic theory

ancient philosophical speculation that all things can be accounted for by innumerable combinations of hard, small, indivisible particles (called atoms) of various sizes but of the same basic material; or the modern scientific theory of matter according to which the chemical elements that combine to form the great variety of substances consist themselves of aggregations of similar subunits (atoms) possessing nuclear and electron substructure characteristic of each element. The ancient atomic theory was proposed in the 5th century BC by the Greek philosophers Leucippus and Democritus and was revived in the 1st century BC by the Roman philosopher and poet Lucretius. The modern atomic theory, which has undergone continuous refinement, began to flourish at the beginning of the 19th century with the work of the English chemist John Dalton. The experiments of the British physicist Ernest Rutherford in the early 20th century on the scattering of alpha particles from a thin gold foil established the Rutherford atomic model of an atom as consisting of a central, positively charged nucleus containing nearly all the mass and surrounded by a cloud of negatively charged planetlike electrons.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
The dyestuffs industry and the chemical industry more generally were the
  products of the atomic theory and what followed from it.
It is as factual an explanation of the universe as the atomic theory of matter
  or the germ theory of disease.
Not unless you also ask whether basic atomic theory is wrong.
Atomic theory offers another example of delayed confirmation.
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