Editing History of atomic theory (section)

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{{Redirect|Atomic model|the unrelated term in mathematical logic|atomic model (mathematical logic)}}
{{about|the historical development of understanding the existence and behavior of atoms|a history of the study of how atoms combine to form molecules|history of molecular theory|the modern view of the atom which developed from atomic theory|atomic physics}}
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[[File:Helium atom QM.svg|right|thumb|200px|The current theoretical model of the atom involves a dense nucleus surrounded by a probabilistic "cloud" of electrons]]
'''Atomic theory''' is the scientific theory that [[matter]] is composed of particles called [[atom]]s. The definition of the word "atom" has changed over the years in response to scientific discoveries. Initially, it referred to a hypothetical concept of there being some fundamental particle of matter, too small to be seen by the naked eye, that could not be divided. Then the definition was refined to being the basic particles of the chemical elements, when chemists observed that elements seemed to combine with each other in ratios of small whole numbers. Then physicists discovered that these particles had an internal structure of their own and therefore perhaps did not deserve to be called "atoms", but renaming atoms would have been impractical by that point.

Atomic theory is one of the most important scientific developments in history, crucial to all the physical sciences. At the start of ''[[The Feynman Lectures on Physics]]'', physicist and Nobel laureate [[Richard Feynman]] offers the atomic hypothesis as the single most prolific scientific concept.<ref name="feynmanleightonsands1963-atomic">{{harvnb|Feynman|Leighton|Sands|1963|p=I-2}} "If, in some cataclysm, all [] scientific knowledge were to be destroyed [save] one sentence&nbsp;[...] what statement would contain the most information in the fewest words? I believe it is&nbsp;[...] that ''all things are made up of atoms&nbsp;– little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another''&nbsp;..."</ref>