From Academic Kids
Arguably, the atomic theory is the single most important theory in the history of science, with wide-ranging implications for both pure and applied science. The theory is credited to John Dalton, a 17th and 18th 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.
In some cases the study of a property at atomic level is very complex and easier results are obtained with a study at a bigger scale. This does not means that atomic theory does not work in these cases. The problem is the mathematical complexities given by treating such problems with the atomic theory. Till nowdays there are no cases where atomic theory does not work, there are only cases in which the result is more easily obtained, in the limit of the wanted approximation, with easier theories. Despite that it may be of some worthness to point out that a general vision should always kept and considered, and to consider the world or the entire universe only as series of atoms is reductive. By SABA MAQSOOD
The existence of atoms was first proposed by Indian philosopher Kanada and Greek philosophers such as Democritus, Leucippus, and the Epicureans, but without any real way to be sure, the concept disappeared until it was revived by Rudjer Boscovich in the 18th century, and after that applied to 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 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.nn:Atomteori