Final answer:
The molecule from the question that shows a difference in bond angle from model predictions is ammonia (NH₃), where the actual bond angle is slightly less than the predicted 109.5° due to the space occupied by the lone pair.
Step-by-step explanation:
The molecule that exhibits a difference in bond angle between real and model structures is ammonia (NH₃). The basic geometry for the ammonia molecule, according to the VSEPR theory, is tetrahedral due to one lone pair and three bonding pairs of electrons around the nitrogen atom. The idealized bond angles for a tetrahedral arrangement are 109.5°. However, in ammonia, the lone pair occupies more space than bonding pairs, resulting in the hydrogen-nitrogen-hydrogen (HNH) bond angles being slightly less than 109.5°.
Water (H₂O) also has two lone pairs and two bonding pairs, leading to a bent shape. The ideal bond angle for tetrahedral geometry is again 109.5°, but due to the repulsion between the lone pairs, the actual bond angle in water is about 104.5°. Methane (CH₄), on the other hand, follows the tetrahedral model closely and has bond angles very close to the predicted 109.5° with no lone pairs to distort the shape.
Carbon dioxide (CO₂) is not included in the original question, but for reference, it is a linear molecule with bond angles of 180°, matching the model predictions as there are no lone pairs to cause deviations.