In all the four cases, the molecules undergo Sp3 hybridization forming four hybrid orbitals, two of which are occupied by 1p of electrons and two by bp electrons. Thus they are expected to have 109°28' angle but this does not happen. In case of H2O molecule, as oxygen is small in size and has high electronegativity value, the bp are closer due to which it is subjected to larger repulsion (bo-bp). In case of H2 S as S atom is larger than O, bp-bp repulsion is less as compared to H2O and it is true for H2 Se and H2 Te as well.
