The molecular structures of alkanes and alkenes differ primarily in the presence of double bonds.

Here's a breakdown:

Alkanes:

* Structure: Contain only single bonds between carbon atoms.

* Formula: General formula is C_nH_2n+2.

* Example: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈)

Alkenes:

* Structure: Contain at least one double bond between carbon atoms.

* Formula: General formula is C_nH_2n.

* Example: Ethene (C₂H₄), Propene (C₃H₆), Butene (C₄H₈)

Key Differences:

* Bonding: Alkanes have only single bonds, while alkenes have at least one double bond.

* Hybridization: The carbon atoms in alkanes are sp³ hybridized, while those in alkenes are sp² hybridized. This affects their bond angles and shapes.

* Reactivity: Alkenes are more reactive than alkanes due to the presence of the double bond, which can undergo addition reactions.

In summary: Alkanes are saturated hydrocarbons with only single bonds, while alkenes are unsaturated hydrocarbons with at least one double bond. This difference in bonding structure leads to significant differences in their chemical properties and reactivity.