Chemistry · Chemical Bonding and Molecular Structure

Assertion (A): The bond angle in water (H2O) is 104.5°, which is less than the tetrahedral angle of 109.5°, and water has a significantly higher boiling point (100°C) than hydrogen sulfide H2S (−60°C) despite H2S having a higher molecular weight. Reason (R): Oxygen in water has two lone pairs that exert greater repulsion on bonding pairs than the lone pairs of sulfur in H2S, compressing the H–O–H bond angle; additionally, the high electronegativity of oxygen (3.5) compared to sulfur (2.5) creates a large dipole moment in water, enabling extensive intermolecular hydrogen bonding that requires significantly more energy to overcome during vaporization.