Question

Why are alkenes unsaturated?

Answer 1

We call an organic compound saturated if all available valence bonds of the `C`'s are bonded to `H` (or other functional groups)

Explanation:

An alkene has a double bond, which means that two of the available bonds are used to bind two `C`'s. This bond can be opened (under the right circumstances) to allow two more `H`'s into the compound.

Compare Ethene: `H_2-C=C-H_2`

With Ethane:`H_3-C-C-H_3`

Ethane has all the `H`'s it can take, and is thus called "saturated"