Science, Tech, Math › Science Geometric Isomer Definition (Cis-Trans Isomers) How Cis-Trans Isomers Work Share Flipboard Email Print The rotation of atoms around a bond produce cis and trans geometric isomers. Todd Helmenstine Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 11, 2018 Isomers are chemical species that have the same chemical formulas, yet are different from each other. For example, learn about geometric isomerization: Geometric Isomer Definition Geometric isomers are chemical species with the same type and quantity of atoms as another species, yet having a different geometric structure. Atoms or groups exhibit different spatial arrangements on either side of a chemical bond or ring structure. Geometric isomerism is also called configurational isomerism or cis-trans isomerism. Note cis-trans isomerism is a different description of geometry than E-Z isomerism. The terms cis and trans are from the Latin words cis, meaning "on this side". and trans, meaning "on the other side". When substituents are both oriented in the same direction as each other (on the same side), the diastereomer is called cis. When the substituents are on opposing sides, the orientation is trans. Cis and trans geometric isomers exhibit different properties, including boiling points, reactivities, melting points, densities, and solubilities. Trends in these differences are attributed to the effect of the overall dipole moment. The dipoles of trans substituents cancel each other out, which the dipoles of cis substituents are additive. In alkenes, trans isomers have higher melting points, lower solubility, and greater symmetry than cis isomers. Identifying Geometric Isomers Skeletal structures maybe be written with crossed lines for bonds to indicate geometric isomers. The IUPAC does not recommend the crossed line notation anymore, preferring wavy lines connecting a double bond to a heteroatom. When known, the ratio of cis- to trans- structures should be indicated. Cis- and trans- are given as prefixes to chemical structures. Examples of Geometric Isomers Two geometric isomers exist for Pt(NH3)2Cl2, one in which the species are arranged around the Pt in the order Cl, Cl, NH3, NH3, and another in which the species are ordered NH3, Cl, NH3, Cl.