Why can fulminic acid and cyanic acid have the same composition but different properties?

Fulminic acid and cyanic acid can have the same composition—meaning they contain the same number and kinds of atoms—yet exhibit different chemical and physical properties because they are isomers.

This phenomenon, which was identified by Justus von Liebig and Friedrich Wöhler, occurs because the atoms in these compounds are arranged or connected differently. In chemistry, isomerism describes molecules that share the same molecular formula but differ in their structural connectivity or spatial orientation.123

Because the specific order of attachment of their constituent atoms varies, each isomer functions as a unique compound with its own distinct characteristics. This discovery was a foundational moment in chemistry, later formally codified by Jöns Jacob Berzelius.31