Final answer:
To name an alkene, identify the longest chain with the double bond, use -ene suffix, and number the chain based on the double bond position. For pentene with a double bond between carbon 2 and 3, it is named 2-pentene. Cis-trans isomerism is indicated by cis- or trans- if substituents are on the same or opposite sides.
Step-by-step explanation:
To name an alkene, one must identify the longest carbon chain containing the double bond and use it as the parent chain. The name of the alkene is based on the stem identical to the alkane with the same chain length, but with an -ene suffix to denote the presence of a double bond. When the chain has more than three carbon atoms, the location of the double bond must be indicated. For pentenes, the double bond can be located starting from the end closest to it, which is denoted by the number of the first doubly bonded carbon. In the case of 2-pentene, the double bond is between the second and third carbon atoms. Additionally, if substituent groups are present, their names and positions are also included in the compound's name. In the presence of geometric isomerism, such as cis-trans isomerism, one must specify the configuration if the substituents are on the same side (cis-) or on opposite sides (trans-) of the double bond.