Relationship between molecule size & boiling point

• A. Molecule size increases - boiling point increases
• B. Molecule size increases - boiling point decreases
• C. Molecule size has no effect on boiling point
• D. Boiling point depends only on mass, not size

Answer: (A)

As molecule size increases, boiling point tends to rise. Larger molecules have more electrons and a bigger surface area, which strengthens London dispersion forces between molecules. These intermolecular attractions are what keep a liquid from boiling, so more energy is needed to overcome them when the molecules are bigger. This is why longer-chain hydrocarbons, for example, boil at higher temperatures than shorter ones. Remember that size often tracks with mass, but other factors matter too: branching can lower the boiling point by reducing surface area, and strong specific interactions like hydrogen bonding can raise boiling points even for smaller or differently shaped molecules. The overall trend is that increasing size generally leads to higher boiling points for similar types of molecules.