In alkenes, the carbon atoms are connected to each other by a what type of bond?

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Alkenes contain a carbon–carbon double bond. This means two carbon atoms share two pairs of electrons: one sigma bond and one pi bond. The sigma bond forms from end-to-end overlap of sp2 hybrid orbitals along the bond axis, giving the main link between the carbons. The pi bond comes from sideways overlap of the remaining p orbitals, lying above and below the plane of the molecule, and it cannot rotate, which fixes the arrangement of substituents and gives cis/trans isomerism. This double bond is responsible for the characteristic reactivity of alkenes, including their tendency to undergo addition reactions that break the pi bond. In contrast, a single bond is typical of alkanes, a triple bond occurs in alkynes, and aromatic bonds involve delocalized electrons in aromatic rings. So the bond between carbon atoms in alkenes is a double bond.