Bigger molecules have more surface area for all those intermolecular forces to play tag. A long-chain hydrocarbon (like octane in gasoline) boils higher than a short one (like propane). Think of it this way: short molecules are sprinting away; long molecules are stuck in traffic. Also, branched molecules boil lower than straight ones—they’re like tangled earphones, unable to pack tight and hold heat.
The Weirdo Exception: Symmetry
Sometimes a perfectly symmetrical molecule (like carbon tetrachloride) has a higher boiling point than a lumpy one, even if it’s non-polar. Why? Symmetry makes it easier for molecules to stack together like Tupperware containers. They snuggle tight, and that takes more energy to separate. Chemistry loves messing with your head.
2.6 Melting Points, Boiling Points, and Intermolecular Interactions
