The boiling point of a substance is influenced by the strength of the interactions between its molecules. Water (H₂O) has a higher boiling point than most alcohols, such as ethanol (C₂H₅OH), despite being a smaller molecule. This might seem counterintuitive at first, but it comes down to the nature of the molecular interactions at play.
The key factor here is hydrogen bonding. Water molecules can form up to four hydrogen bonds with neighboring water molecules due to their polar nature and bent shape. This strong intermolecular force requires a significant amount of energy to overcome, which is reflected in water’s high boiling point of 100°C (212°F) at standard pressure.
On the other hand, while alcohols can also form hydrogen bonds, they do so to a lesser extent than water. Ethanol, for instance, can form hydrogen bonds, but it has a hydrocarbon chain attached to its hydroxyl group (-OH) which makes its overall structure less polar and subsequently leads to weaker intermolecular forces compared to water. As a result, alcohols like ethanol have a boiling point of around 78°C (172°F).
In summary, even though water is a smaller molecule than alcohols, the presence of extensive hydrogen bonding in water significantly raises its boiling point. This demonstrates how molecular interactions can profoundly influence physical properties like boiling points.