International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What characterizes an unsaturated compound?

1. A molecule containing only single bonds

2. A molecule containing a carbon-carbon bond

3. A molecule without hydrogen atoms

4. A molecule with no carbon atoms

The correct answer is: A molecule containing a carbon-carbon bond

An unsaturated compound is characterized by the presence of one or more carbon-carbon multiple bonds, such as double or triple bonds. These types of bonds create a scenario where the molecule can incorporate additional hydrogen atoms, meaning it does not have the maximum possible number of hydrogen atoms for a given number of carbon atoms. When considering the options, the presence of a carbon-carbon bond that can be multiple bonded (especially a double or triple bond) indicates unsaturation. This contrasts with saturated compounds, which contain only single bonds between carbon atoms and therefore hold the maximum hydrogen atoms possible for the number of carbon atoms present. While other choices might suggest some form of bonding or composition, they do not correctly define unsaturation. For instance, molecules with only single bonds are saturated, while those without hydrogen atoms or carbon atoms are not relevant to the definition of unsaturation in organic chemistry. Hence, the presence of a carbon-carbon bond that is characteristic of unsaturation is the defining feature of the compound described as unsaturated.