Question

Indicate whether organic halides have boiling points that are generally higher, lower, or similar to those of the following. (Assume that the molecular mass is comparable.) (a) alcohols (b) hydrocarbons

Short answer

Organic halides have boiling points lower than alcohols but higher than hydrocarbons with similar molecular masses.

Step-by-step solution

Understanding Organic Halides and their Properties

Organic halides, also known as alkyl halides, are compounds where a halogen atom (such as chlorine, bromine, or iodine) is bonded to an alkyl group. These compounds generally have intermediate boiling points because they are polar due to the presence of electronegative halogen atoms, but they do not have hydrogen bonding.

Comparing Boiling Points with Alcohols

Alcohols have the functional group -OH, which can engage in hydrogen bonding. Hydrogen bonds are strong intermolecular forces that significantly increase boiling points. Therefore, alcohols typically have higher boiling points compared to organic halides of similar molecular weight due to this additional hydrogen bonding.

Comparing Boiling Points with Hydrocarbons

Hydrocarbons consist solely of carbon and hydrogen and are generally non-polar, leading to weaker van der Waals forces and thus lower boiling points compared to organic halides. Without strong intermolecular forces like hydrogen bonding present in alcohols, hydrocarbons have generally lower boiling points than organic halides of similar molecular mass.

Key concepts

Boiling Points

Boiling point refers to the temperature at which a liquid turns into vapor. It's a crucial property in chemistry because it gives insight into the strength of intermolecular forces present within a substance. Substances with strong intermolecular forces usually have higher boiling points because more energy is needed to break these forces and transition to the gaseous phase. Among different classes of compounds, those capable of hydrogen bonding, like alcohols, tend to have the highest boiling points. On the other hand, organic halides, which contain a halogen atom, generally have intermediate boiling points due to their polar nature but lack of hydrogen bonds. In contrast, hydrocarbons, which are non-polar, exhibit lower boiling points since they rely solely on weaker van der Waals forces.

Organic Halides

Organic halides, or alkyl halides, are a fascinating class of organic compounds. They are derived from hydrocarbons, where one or more hydrogen atoms are replaced by halogen atoms such as fluorine, chlorine, bromine, or iodine. This substitution imparts distinct physical and chemical properties to these compounds.
One significant aspect of organic halides is their intermediate boiling points. The presence of the electronegative halogen atom induces a polar bond, introducing dipole-dipole interactions. These interactions are stronger than the van der Waals forces found in non-polar hydrocarbons, yet they are typically weaker than the hydrogen bonds in alcohols.
Because of these polar interactions, organic halides have boiling points that are generally higher than hydrocarbons but lower than alcohols, assuming similar molecular masses.

Intermolecular Forces

Intermolecular forces play a pivotal role in dictating the physical properties of substances, including their boiling points. These forces are the attractions between molecules and come in various strengths depending on the type of force.

• Dispersion Forces: Also known as London dispersion forces, they occur in all molecules but are the only type in non-polar molecules like hydrocarbons. They are the weakest intermolecular force.
• Dipole-Dipole Interactions: Present in polar molecules like organic halides, these forces arise from the electrostatic attraction between positive and negative dipoles.
• Hydrogen Bonds: The strongest of the three, these forces occur when a hydrogen atom bonded to a highly electronegative atom such as oxygen exhibits an attraction to another electronegative atom. This is why alcohols have higher boiling points.

By understanding these interactions, it becomes easier to predict and comprehend why certain substances like alcohols have higher boiling points compared to organic halides, which in turn are higher than hydrocarbons.