Final answer:
The strength of intermolecular forces in water is greater than in ammonia due to water's ability to form four hydrogen bonds compared to ammonia's two, contributing to water's higher boiling point and stronger physical properties.
Step-by-step explanation:
When discussing the relative strengths of intermolecular forces between ammonia (NH3) and water (H2O) molecules, it's important to consider the types of forces involved. Both ammonia and water participate in hydrogen bonding, which is a strong type of dipole-dipole interaction occurring between molecules that have a hydrogen atom bonded to a very electronegative atom like nitrogen (in the case of ammonia) or oxygen (in the case of water).
In water molecules, each molecule can form up to four hydrogen bonds due to the presence of two hydrogens and two lone pairs on the oxygen atom, which leads to a very high boiling point compared to other substances of similar molecular mass. Ammonia, on the other hand, can form, on average, only two hydrogen bonds at a time, since each molecule has one nitrogen with a lone pair and three hydrogens. Consequently, ammonia has a lower boiling point than water. The electronegativity of oxygen in water also contributes to stronger hydrogen bonds compared to the nitrogen in ammonia. This difference in hydrogen bonding capabilities is a key factor in the physical properties of these substances, like boiling points and surface tension.