Isomer
/ˈaɪ.sə.mər/noun
A compound or molecule with the same chemical formula as another but a different arrangement of atoms and therefore often different properties.
Did you know?The term was introduced in the 1830s after chemists discovered that substances with identical elemental compositions could possess radically different properties.
Etymological Timeline
Proto-Indo-European
PIE
*sem-
“One; together; same—an ancestral root associated with sameness and unity.”
Ancient Greek
Greek
isos (ἴσος)
“Equal; same.”
Ancient Greek
Greek
meros (μέρος)
“Part; portion.”
1830s
German
Isomerie / isomer
“A term coined in early modern chemistry for substances having the same composition but different properties or structures.”
19th Century
English
isomer
“A substance with the same chemical composition as another but a different molecular arrangement.”
Modern English
English
isomer
“A molecule or compound sharing a molecular formula with another while differing in atomic arrangement.”