Final answer:
The bond angle between hydrogen atoms in the H2O molecule is approximately 104.5° due to the lone pairs on the oxygen atom occupying more space and compressing the bond angle from the ideal tetrahedral angle.
Step-by-step explanation:
If you were to construct the molecule H2O using a molecular kit, you should arrange the atoms to display the correct bond angles in the structure. Quantum-mechanical calculations, involving the wave function and hybrid orbitals, more accurately explain real-world observations than simple p-orbital interactions. The oxygen atom in a water molecule uses sp3 hybrid orbitals to bond with hydrogen, which predicts a tetrahedral bond angle of 109.5°. However, due to the larger space occupied by the lone pairs, the bond angle between hydrogen atoms in H2O is actually compressed to approximately 104.5°.