cis and trans prefix's to molecules

[Emily Kennedy 4L]

How do you know when to use the cis and trans prefixes?

[Venya Vaddi 1L]

These prefixes are used when naming isomers. Cis means same side and trans means on the other side. I don't think we need to know this nomenclature since we have not covered it yet.

[Jovian Cheung 1K]

Double bonds prevent rotation.

So imagine a molecule like C₂H₂Cl₂ (search up the structure and you'll see images of the isomers, including the cis and trans ones), where the two C are double bonded and there is one Cl and one H on each C.

The isomer where both Cl are on the same side is the cis isomer, and the isomer where the two Cl are on different sides of the double bond is the trans isomer. :-)
This is the basic idea.

When more different elements are involved in the molecule, there are more complicated rules (involving electronegativity, if I remember correctly). There's also other ways of classifying isomers, e.g. E/Z isomerism.

But that's the basic idea for cis/trans so far!