Final answer:
Geometric isomers occur when the order of atom bonding is the same but the arrangement of atoms in space is different. Alkenes can form geometric isomers because the double bond in an alkene is rigid, preventing rotation. In contrast, alkanes cannot form geometric isomers because their single bonds allow for free rotation.
Step-by-step explanation:
Geometric isomers are isomers in which the order of atom bonding is the same but the arrangement of atoms in space is different. Alkenes can form geometric isomers because the double bond in an alkene is rigid and does not allow for free rotation. This means that the two carbon atoms in an alkene can have different groups attached to them on either side of the double bond, resulting in different geometric isomers.
For example, in 2-pentene, there are two possible geometric isomers: cis-2-pentene and trans-2-pentene.
In cis-2-pentene, the two methyl groups are on the same side of the double bond, while in trans-2-pentene, the two methyl groups are on opposite sides of the double bond.
In contrast, alkanes cannot form geometric isomers because the carbon-carbon single bond in alkanes allows for free rotation, which means that the arrangement of atoms in space remains the same.