Like water, hydrogen fluoride, HF, and ammonia, NH3, have relatively high boiling points. Explain.
A.The polar molecules of each of these materials have relatively strong attractions for themselves, which translates to relatively high boiling points.
B. Since these molecules interact with each other in long chains, they have many regions of attraction and are held together relatively tightly, thus, they are harder to pull apart when boiling.
C. Since these are all relatively small molecules, they can compact more tightly together, and will require more energy to be separated from each other.
The correct explanation for the relatively high boiling points of water, hydrogen fluoride (HF), and ammonia (NH3) is option A. The polar molecules of each of these materials have relatively strong attractions for themselves, which translates to relatively high boiling points.
To understand why this is the case, we need to consider the intermolecular forces between the molecules. In water, HF, and NH3, the oxygen, fluorine, and nitrogen atoms respectively, are more electronegative than the hydrogen atom, resulting in a polar covalent bond. This means that there is an uneven distribution of charge within the molecule, with the oxygen, fluorine, and nitrogen atoms having a partial negative charge, and the hydrogen atom having a partial positive charge.
These partial charges create dipole-dipole attractions between neighboring molecules. The positive end of one molecule is attracted to the negative end of another molecule, creating relatively strong forces of attraction between the molecules. These dipole-dipole attractions are collectively known as hydrogen bonding in the case of water and HF, and as dipole-dipole forces in the case of NH3.
Due to these relatively strong intermolecular forces, more energy is required to break the attractive forces and convert the substance from a liquid to a gas during boiling. Therefore, water, HF, and NH3 have higher boiling points compared to substances with weaker intermolecular forces.
Option B suggests that the molecules of water, HF, and NH3 interact with each other in long chains, resulting in many regions of attraction and tight bonding. However, this explanation does not accurately describe the intermolecular forces at play, as hydrogen bonding and dipole-dipole forces are responsible for the strong attractions, rather than chains of molecules.
Option C states that because these molecules are relatively small, they can compact more tightly together, requiring more energy to separate from each other. While the size of molecules can affect their boiling points, it is not the primary factor in the case of water, HF, and NH3. The dominant factor is the strength of the intermolecular forces, as explained in option A.