Why H-O-H bond angle in a water molecule is greater than H-S-H bong angle in H2S molecule?

Ans. The central atom of H₂O is O and H₂S is S. Due to the smaller size of oxygen, the electronegativity of oxygen is greater than that of S. In H₂O molecule, the central atom of oxygen has four electron pairs in which two pairs are bonding pairs and two pairs are lone pairs. In H2S molecules, central atom S also has four pairs with two pairs bonding pairs and two pairs lone pairs. So, generally both bond angles H-O-H and H-S-H are expected to be the same but due to the higher electronegativity of oxygen than that of sulphur, the H-O-H bond angle in water molecules becomes comparatively higher than that of H-S-H bond angle in H₂S molecule.