Atomic Theory

This a umes that matter is not infinitely divisible; that it is made up of indivisible particles which we call atoms; that when combination takes place between two or more elements, it is the atoms of each which first combine; that the atoms of the same element are alike, and different from those of any other element; and that the atoms of each element have a definite weight which is unlike that of the other elements. These a umptions are made in order to explain the Law of Definite Proportions, that a given chemical compound always contains the same elements in the same proportion, and the Law of Multiple Proportions, that when two elements, A and B, unite to form several compounds with each other, the relative quantities of B which combine with any fixed quantity of A bear a simple ratio to one another. The theory was proposed by Dalton in 1804. It is the fundamental theory of modern chemistry, and is almost universally accepted.