Dalton's atomic theory

In an attempt to explain how and why elements combine with one another in the fixed ratios and at times also in multiples of those ratios, Dalton formulated the atomic theory. He said that the reason elements differed from each other was that atoms of each element were different from each other; particularly, they had different masses.

He said that compounds consisted of the atoms of different elements combined together. Compounds are pure substance as the atoms of different elements are bonded to one another. Compounds have constant composition because they contain a fixed ratio of atoms and each atom has its own characteristic weight, therefore fixing the weight ratio of one element to the other. In addition he said that chemical reactions involved the rearrangement of combinations of those atoms Dalton's model was that the atoms were tiny, indivisible, indestructible particles and that each one had a certain mass, size, and chemical behavior that was determined by what kind of element they were.

Modern atomic theory is, of course, a little more involved than Dalton's theory but the essence of Dalton's theory remains valid. Also, there are different kinds of atoms within an element that is known as "isotopes", but isotopes of the element have same chemical properties.

Atoms are indestructible and indivisible. All the atoms of the given element are same in the mass and properties. Compounds are formed by the mixture of 2 or more different kinds of atoms. A chemical reaction is a rearrangement of the atoms.