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Creative Chemistry Molecular Models

Isomers Department

What are isomers?

Isomers are molecules with the same molecular formula, but different arrangements of atoms. There are different types of isomers, shown by the diagram on the right.

Select a type of isomer to find out more about it and to see molecular models of examples.

Find out more about isomers at Isomers Totally Explained.

Find out about geometrical isomerism



Structural Isomerism

Structural isomerism occurs when two or more organic compounds have the same molecular formulae, but different structures. These differences tend to give the molecules different chemical and physical properties. There are three types of structural isomerism that you need to be aware of at school: chain isomerism, positional isomerism and functional isomerism. There is a fourth type, known as tautomerism (where there are two isomers are known as the keto and enol isomers) but you won’t come across this at school.


Stereo-isomerism occurs when the atoms in a molecule can have different arrangements in space. There are two types of stereo-isomerism: geometrical isomerism and optical isomerism. Geometrical isomers can have very different physical properties, such as different melting points, but they tend to have the same chemical properties. Optical isomers have the same chemical and physical properties, except that one structure rotates the plane of polarised light to the right and the other rotates it to the left.

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