The main postulates are: 1. Matter is composed of microscopic indivisible particles called "Atom". i. This has since been shown to be false 2. Atom can neither be created nor it is destroyed. 3. Atoms of an element are identical in size, shape, mass and in other properties. i. Isotopes are a counterpoint to this postulate 4. Atoms of different elements are different in their properties. 5. Atoms combine with each other in small whole number ratios. i. Sugar molecule C_{12} H_{22} O_{11} is a counterpoint to this postulate 6. All chemical reactions are due to combination or separation of atoms.

When you crush a lump of sugar, you can see it is made up of smaller particles of sugar. You can grind these particles but each one of them is still sugar. Observations like this led to earlier philosophers to ponder into the fundamental theory of matter.Scientists began gathering evidence favoring the atomic theory of matter. John Dalton based his atomic theory on the law of conservation of mass, the law of definite proportions and the law of multiple proportions. John Dalton reasoned that elements were composed of atoms and that only whole number of atoms can combine to form compounds. His theory can be summed up by the following statements: 1. All matter is composed of extremely small particles called atoms. 2. Atoms of an element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. 3. Atoms cannot be subdivided, created or destroyed. 4. Atoms of different elements combine in simple whole number ratios to form chemical compounds. 5. In chemical reactions, atoms are combined, separated or rearranged. Not all aspects of Dalton's atomic theory have proven to be correct. The important concepts that 1. All matter is composed of atoms and 2. Atoms of any one element differ from the properties of another element remain unchanged. Dalton's atomic theory has not been discarded only modified.