What is generally true about boiling points regarding molecular weight?

What is generally true about boiling points regarding molecular weight?

• A. Boiling points decrease with increasing molecular weight
• B. Boiling points are unaffected by molecular weight
• C. Boiling points usually increase as molecular weight increases
• D. All compounds have the same boiling point regardless of weight

Answer: (C)

Boiling points generally tend to increase with molecular weight primarily due to the nature of intermolecular forces. As molecular weight increases, molecules typically have more electrons and a larger electron cloud, which can lead to stronger London dispersion forces (a type of van der Waals force) between them. These intermolecular forces are significant contributors to the boiling point of a substance, as stronger forces require more energy to overcome, thus leading to higher boiling points. For example, consider a series of alkanes: as you move from methane (CH₄) to octane (C₈H₁₈), the molecular weight increases, and so does the boiling point. This trend observed is often consistent across various families of compounds despite variations in molecular structure. Other factors can influence boiling points, such as branching in hydrocarbons or the presence of functional groups; however, the general trend is that an increase in molecular weight correlates with higher boiling points.

Boiling points generally tend to increase with molecular weight primarily due to the nature of intermolecular forces. As molecular weight increases, molecules typically have more electrons and a larger electron cloud, which can lead to stronger London dispersion forces (a type of van der Waals force) between them. These intermolecular forces are significant contributors to the boiling point of a substance, as stronger forces require more energy to overcome, thus leading to higher boiling points.

For example, consider a series of alkanes: as you move from methane (CH₄) to octane (C₈H₁₈), the molecular weight increases, and so does the boiling point. This trend observed is often consistent across various families of compounds despite variations in molecular structure.

Other factors can influence boiling points, such as branching in hydrocarbons or the presence of functional groups; however, the general trend is that an increase in molecular weight correlates with higher boiling points.