Question

$H_2O$ is a liquid while $H_2S$ is a gas. Why?

Hint:

Hydrogen bonding significantly increases boiling points of molecules like $H_2O$, $HF$, and $NH_3$.

Answer 1

Step 1: Nature of intermolecular forces.
- In $H_2O$, due to the high electronegativity of oxygen, strong intermolecular hydrogen bonding is present.
- In $H_2S$, sulphur is less electronegative, and hence hydrogen bonding is absent. Only weak van der Waals forces are present.
Step 2: Effect of intermolecular forces.
- Strong hydrogen bonding in $H_2O$ holds the molecules together, giving it a liquid state at room temperature.
- Weak forces in $H_2S$ cannot hold molecules strongly, so it exists as a gas at room temperature.
Conclusion:
$H_2O$ is liquid due to strong hydrogen bonding, while $H_2S$ is gas due to weak van der Waals forces.