Some ions or molecules have identical formulas but different structures; these are called isomers. Because they have identical formulas, each isomer contains the same number of atoms though their atomic arrangement would be different. Let’s take a look at glucose and fructose. Both glucose and fructose have the same chemical formula but they have two distinct structures.
Friedrich Wohler was the first to notice this phenomenon. In 1827, Wohler realised while preparing silver cyanate that despite having the same elemental composition as silver fulminate, its properties were entirely different. Wohler’s discovery challenged the prevailing chemical understanding.
Isomerism was accepted widely after similar discoveries were made. For example, Wohler himself discovered another pair of compounds-urea and ammonium cyanate in 1828. They too had same atomic compositions but were chemically distinct. Jons Jacob Berzelius introduced the term isomerism to describe this phenomenon.
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