9.13C - Why alkenes are unsaturated

Recognising the alkene functional group

A hydrocarbon contains carbon and hydrogen only. An alkene is an unsaturated hydrocarbon containing a carbon–carbon double bond, written $\ce{C=C}$.

A functional group is the atom or group of atoms responsible for the characteristic reactions of an organic family. The alkene functional group is C=C. It must be a double bond between two carbon atoms: $\ce{C=O}$ is a carbon–oxygen double bond, not the alkene functional group.

[DIAGRAM: asset_name: c_c_functional_group: The C=C functional group in an alkene - diagram 1; asset_slug: 217_9_13c_alkenes_are_unsaturated_hydrocarbons_describing_that_their_molecules_conta_diagram1; file: 217_9_13c_alkenes_are_unsaturated_hydrocarbons_describing_that_their_molecules_conta_diagram1.png; recommended_method: deterministic_drawn; description: Monochrome deterministic structure-support diagram showing a simple supplied alkene example with H2C=CH2, the C=C double bond circled or bracketed, labels "carbon-carbon double bond", "alkene functional group" and "hydrocarbon: C and H only". Exact assessed concept visual; white background, #6A6B6E linework/text only, no colour coding, no bromine, no addition reaction, no polymerisation and no formula-recall table.]