 The situation was made more complex when chemists realized that elemental composition was not in general sufficient to distinguish substances. Dalton was aware that the same elements sometimes give rise to several compounds; there are several oxides of nitrogen, for example. But given the law of constant proportions, these can be distinguished by specifying the combining proportions, which is what is represented by distinct chemical formulas, for example N2O, NO and N2O3 for different oxides of nitrogen. However, as more organic compounds were isolated and analyzed, it became clear that elemental composition doesn’t uniquely distinguish substances. Distinct compounds with the same elemental composition are called isomers. The term was coined by Berzelius in 1832 when organic compounds with the same composition, but different properties, were first recognized. It was later discovered that isomerism is ubiquitous, and not confined to organic compounds.