Why is water a liquid at room temperature?

• A. Weak intermolecular forces
• B. Strong covalent bonds
• C. Large molecular mass
• D. Ionic bonds

Answer: (A)

The key idea is how strong the attractions are between different water molecules. Water molecules themselves are held together by strong covalent bonds inside the molecule, but the forces that hold separate water molecules together are hydrogen bonds, a type of intermolecular force. These intermolecular forces are weaker than the covalent bonds within a molecule, yet they’re strong enough to keep water in a liquid state at room temperature. If the intermolecular attractions were much weaker, water would be a gas; if they were much stronger, it could be a solid at the same temperature. So at room temperature, the moderate intermolecular attractions between water molecules make it a liquid. The other options point to causes that aren’t responsible for water’s state: covalent bonds are within a molecule, not between molecules; molecular mass isn’t the deciding factor for this state; and ionic bonds don’t apply to liquid water.