Question

the stronger the intermolecular forces, the more strongly molecules are attracted to each other and the higher the temperature required to overcome those attractions and allow the substance to boil. take a look at the boiling point graph to the right. remember that the strength of the london forces increases with the increase in molecule size. based on the graph, hf has the highest boiling point but is the smallest molecule. what type of imf is present in hf and not present in the other molecules that might account for this? hydrogen bonding covalent bonding induced dipoles induced dipole - induced dipole

Explanation:

• Hydrogen bonding: This is a special type of dipole - dipole interaction. It occurs when a hydrogen atom is bonded to a highly electronegative atom (such as F, O, or N). In HF, the H - F bond is highly polar. The hydrogen atom in one HF molecule is attracted to the fluorine atom in another HF molecule. This strong intermolecular force (hydrogen bonding) leads to a higher boiling point.
• Covalent bonding: This is an intramolecular force (a bond within a molecule), not an intermolecular force (a force between molecules). So it does not affect the boiling point (which is related to intermolecular forces).
• Induced dipoles (London forces): These are the weakest intermolecular forces. They are based on the temporary distortion of electron clouds. While they exist in all molecules, in the case of HF, hydrogen bonding is a much stronger force that dominates the boiling - point behavior. For the other hydrogen halides (HCl, HBr, HI), London forces are the main intermolecular forces (since they do not have hydrogen bonding), and their strength increases with molecular size (as the problem statement mentions that London force strength increases with molecular size). But HF has hydrogen bonding which makes its intermolecular forces stronger than what would be predicted by its small size based on London forces alone.
• Induced dipole - induced dipole (also London forces): As explained above, these are weak forces and do not account for the high boiling point of HF compared to its small size.

Answer:

Hydrogen bonding