GCSE CHEMISTRY - What is an Alkene? - Structure - Unsaturated - Homologous Series - Structural Formula

What is an Alkene?

Alkenes form an homologous series with the
general formula C_nH_2n.

Methene, CH₂, does not exist.	Butene, C₄H₈, has n=4.
Ethene, C₂H₄, has n=2.	Pentene, C₅H₁₀, has n=5.
Propene, C₃H₆, has n=3.	Hexene, C₆H₁₂, has n=6.

Below are links to the structure of alkenes.
Some of these exist as isomers.

Ethene Propene

Butene Pentene Hexene

Alkenes are hydrocarbons which have at least one
double bond between two of the carbon atoms.
They do not have the maximum number of hydrogen atoms
for the number of carbon atoms present
(they have two less than the same alkane)
and so alkenes are called unsaturated hydrocarbons.