Problem 82 - Chemistry: The Central Science

Question

(a) What is meant by the term isomer? (b) Among the four alkanes, ethane, propane, butane, and pentane, which is capable of existing in isomeric forms?

Step-by-Step Solution

Answer

(a) An isomer refers to a compound with the same molecular formula as another compound but with a different structural arrangement of the atoms, leading to distinct physical and chemical properties. (b) Among the four given alkanes, both butane (\(C_4H_{10}\)) and pentane (\(C_5H_{12}\)) are capable of existing in isomeric forms.

Step 1: Part (a): Definition of Isomer

An isomer refers to a compound with the same molecular formula as another compound but with a different structural arrangement of the atoms. In other words, isomers are molecules that have the same number of atoms of each element, but the atoms are arranged in a distinct way, leading to different physical and chemical properties.

Step 2: Part (b): Identifying Alkane with Isomeric Forms

Let's analyze each of the given alkanes to check if they are capable of existing in isomeric forms. 1. Ethane: \(C_2H_6\) - Ethane has two carbon atoms and a single possible structural arrangement, thus it has no isomeric forms. 2. Propane: \(C_3H_8\) - Propane has three carbon atoms and, like ethane, has only one possible structural arrangement. So, it also has no isomeric forms. 3. Butane: \(C_4H_{10}\) - Butane has four carbon atoms, and there are two possible structural arrangements for this molecule: n-butane (normal butane), where all carbon atoms are in a straight chain, and iso-butane (2-methylpropane), where three carbon atoms are in a chain, and the fourth is connected to the second carbon in the chain. As there are two possible arrangements, butane has isomeric forms. 4. Pentane: \(C_5H_{12}\) - Pentane has five carbon atoms, and there are three possible structural arrangements: n-pentane (normal pentane), isopentane (2-methylbutane), and neopentane (2,2-dimethylpropane). As there are three possible arrangements, pentane also has isomeric forms. Among the four given alkanes, both butane and pentane are capable of existing in isomeric forms.