  The key assumption of Dalton's chemical atomism is that chemical elements are composed of ‘ultimate particles’ or atoms. The least part of a chemical compound is assumed to be made up of characteristic combinations of atoms of the component elements. Dalton called these ‘compound atoms’. According to Dalton, all atoms of a given substance whether simple or compound, are alike in shape, weight and any other particular. This much already entails the law of constant proportions. Although Dalton himself resisted the move, Berzelius was able to show how Dalton's theory can be conveniently portrayed by representing the composition of compounds in terms of elements by chemical formulae in the way that has since become commonplace. Hereafter this device is employed using modern conventions rather than any of the various ones used by Berzelius and his contemporaries,