Final answer:
Water, H₂O, has stronger intermolecular forces than ammonia, NH₃, because of the hydrogen bonds that result from water's polar nature. These forces give water its high boiling point, surface tension, and make ice less dense than its liquid form.
Step-by-step explanation:
When comparing intermolecular forces of attraction, it is clear that water, H₂O, exhibits stronger forces than ammonia, NH₃. This is due to the strong hydrogen bonds present in water molecules where an H atom is covalently bonded to a highly electronegative O atom, leading to a significant positive and negative dipole within the molecule. These dipoles, in turn, lead to the formation of strong hydrogen bonds between different water molecules, resulting in high boiling and melting points, high surface tension, and water's ability to act as a versatile solvent. Ammonia also forms hydrogen bonds due to its N-H bonds but to a lesser extent, contributing to its lower boiling point than water and weaker overall intermolecular attractions.
Intermolecular forces also account for certain phenomena such as water's anomalous expansion when freezing, leading to ice having a lower density than liquid water as evidenced by Figure 10.2.2. It's also crucial to recognize temperature's influence on these forces. As temperature increases, the kinetic energy of the molecules also increases which leads to a reduction in the effects of intermolecular forces, as highlighted in Effect of Temperature on Intermolecular forces. Conversely, at lower temperatures, molecules have less kinetic energy and the forces holding them together dominate, causing the substance to maintain a less fluid state.