The alkenes are very similar to the alkanes except they are from a different homologous series (i.e. has different chemical properties and general formula to alkanes). If anyone asks what the difference between the alkanes and they alkanes is (in the post office or supermarket for instance) do not say one letter. If you do, you will be dragged through the streets and publicly mocked – it is an old joke. There are actually three main differences (excluding you know what):  

1.      Different chemical properties

2.      Different general formula

3.      Alkanes contain a C-C double bond

The first two you already know. Alkanes and alkenes are form different homologous series. The second and third we’ll just come to.                                                                                          A double bond is where two carbons form two bonds between each other. We use two lines to represent a double bond. It looks like this:

C=C

How many bonds can carbon form? Four. So each of these carbons can form two more bonds. Thus, each carbon can form two bonds with hydrogen so it forms four bonds. This would give us the first member of the alkenes which is ethene: