What type of hydrocarbons are alkenes and alkynes classified as?

Alkenes and alkynes are classified as unsaturated hydrocarbons because they contain carbon-carbon double or triple bonds, respectively. The presence of these multiple bonds reduces the number of hydrogen atoms that can be bonded to the carbon skeleton compared to saturated hydrocarbons, which only have single bonds between carbon atoms and are fully 'saturated' with hydrogen.

In the case of alkenes, the presence of at least one double bond between carbon atoms indicates that not all available bonding sites for hydrogen are utilized. Similarly, alkynes have one or more triple bonds, further decreasing the number of hydrogen atoms attached to the carbon atoms. This characteristic is what defines them as unsaturated hydrocarbons, as they can potentially react with additional hydrogen or other atoms to achieve a saturated state.

The other classifications do not apply here. Saturated hydrocarbons lack double or triple bonds and are fully bonded with hydrogen. Acyclic hydrocarbons refer to those that do not form ring structures, while cyclic hydrocarbons involve closed ring formations. Alkenes and alkynes can be found in both acyclic and cyclic forms, but their classification as unsaturated is fundamental due to their bonding nature.