Question

Explain the following observation:

Among the hydrides of elements of group 16, water shows unusual physical properties.

Answer 1

Explanation for unusual physical properties of water (H₂O) among group 16 hydrides:

1. Water is a liquid at room temperature, unlike other group 16 hydrides (H₂S, H₂Se, H₂Te) which are gases.
2. Water has a much higher boiling point due to strong intermolecular hydrogen bonding between H₂O molecules.
3. Hydrogen bonding requires extra energy to break, raising water’s boiling point and reducing its volatility.
4. Other hydrides lack hydrogen bonding due to the lower electronegativity of central atoms; their intermolecular forces are weaker van der Waals forces.
5. The volatility order is H₂O < H₂S > H₂Se > H₂Te, opposite to expectation based on molecular masses.
6. Water’s high thermal stability and low acidity also relate to hydrogen bonding in it.

Thus, hydrogen bonding in water causes its unusual physical properties compared to other group 16 hydrides.