You're right to be curious about this! While both water (H₂O) and ammonia (NH₃) are small molecules, they have very different properties at room temperature. This difference boils down to the strength of the forces holding the molecules together:

Hydrogen Bonding:

* Water: Water molecules are very polar, meaning they have a positive end (the hydrogen atoms) and a negative end (the oxygen atom). These opposite charges allow water molecules to form strong hydrogen bonds with each other. These bonds are very strong and require a lot of energy to break, explaining why water remains a liquid at room temperature.

* Ammonia: Ammonia also has a polar structure and forms hydrogen bonds, but they are weaker than those in water. This is because the nitrogen atom in ammonia is less electronegative than the oxygen atom in water, meaning it doesn't pull as strongly on the shared electrons. Weaker hydrogen bonds mean less energy is needed to break them, so ammonia exists as a gas at room temperature.

Other Factors:

* Molecular Weight: While not as significant as hydrogen bonding, ammonia has a lower molecular weight than water, which also contributes to its volatility (tendency to vaporize).

In summary: The key difference lies in the strength of hydrogen bonding. Water's stronger hydrogen bonds lead to a higher boiling point and a liquid state at room temperature, while ammonia's weaker hydrogen bonds result in a lower boiling point and a gaseous state at room temperature.