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Which type of carbon-carbon bond occurs in an alkene?

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structures of common hydrocarbon compounds — hydrocarbon Structures assumed by hydrogen (H) and carbon (C) molecules in four common hydrocarbon compounds.

Alkenes are characterized by the presence of a carbon-carbon double bond.123

This double bond is a type of covalent bond composed of two distinct components:45

Sigma ( $σ$ ) bond: One pair of shared electrons forms a $σ$ bond, which serves as the primary connection between the carbon atoms.243
Pi ( $π$ ) bond: The second pair of electrons occupies regions above and below the plane of the $σ$ bond, forming a pi ( $π$ ) bond.245

Because this double bond contains a $π$ bond, which is a region of increased electron density, alkenes are considered unsaturated hydrocarbons. These electrons are more distant from the carbon nuclei than those in the $σ$ bond, making them more reactive and susceptible to addition reactions.1234