Final answer:
NH3 molecules primarily experience hydrogen bonding due to nitrogen's high electronegativity, leading to strong dipole-dipole attractions between hydrogen and nitrogen atoms of adjacent molecules, as well as London Dispersion Forces which are weaker and present in all molecules.
Step-by-step explanation:
The intermolecular forces present in a pure sample of NH3 (ammonia) can be determined by examining the Lewis Dot structure. In the case of NH3, the molecule consists of a nitrogen atom bonded to three hydrogen atoms. The nitrogen is more electronegative than the hydrogen, generating a polar bond. These polarities lead to an unequal distribution of electrons, which results in a permanent dipole.
Hydrogen bonding is the primary intermolecular force in NH3, due to the presence of a highly electronegative nitrogen atom bonded to hydrogen. This electronegativity difference gives rise to a strong dipole-dipole interaction when the hydrogen atom, which carries a partial positive charge, forms an attraction with a lone pair on a nitrogen atom of an adjacent NH3 molecule. However, NH3 molecules also exhibit London Dispersion Forces (LDF), which are present in all molecules and increase as molecules become larger.