Question

ICl has a higher boiling point than Br2. What is the best explanation for this?
Br2 experiences dipole-dipole interactions.
ICl experiences dipole-dipole interactions.
Br2 forms hydrogen bonds.
ICl experiences induced dipole-induced dipole interactions.

Answer 1

maybe B or C

Answer 2

Dipole-Dipole interactions are the electrostatic attractions between the positive and negative ends of molecules. They result from molecules where one of the atoms has a greater electronegativity, or attraction for the shared pair/pairs of electrons between the atoms, that any of the others. In such a case, the electrons will be drawn towards this most electronegative atom, leaving it with what we call a partial/temporary negative charge (negative dipole). Subsequently, as this atom has drawn the shared electrons further away from the other atom/atoms in the molecule, these remaining atoms will have a partial positive charge (positive dipole). Thus, as a liquid where the individual molecules are free to interact with each other, we get a dipole-dipole attraction between the positive end of one molecule and the negative end of another. This adds an extra barrier to overcome in forming a gas, requiring extra energy or heat to overcome and resulting in a higher boiling point as it turns from a liquid to a gas.

Let's take ICl, for example. Iodine (I) and chlorine (Cl) are both in group 7 of the periodic table. We know that electronegativity decreases as you go down a group, and so Cl will have a greater attraction for the pair of shared electrons that forms the bond between it and I. So, as described before, we will get a dipole forming due to this and thus dipole-dipole interactions can occur between identical ICl molecules. As the bromine atoms in Br2 are identical, the shared electrons that form the bond between the atoms are not pushed towards one or the other, as both have an equal attraction for them. Hence, no dipole can occur and these electrostatic interactions between the molecules cannot be seen with Br2. Thus, this is why you would expect ICl to have a higher boiling point than Br2.

-Br2 cannot form hydrogen bonds, as these are special polar interactions between the hydrogen of one molecule and either the oxygen, fluorine or nitrogen of another molecule, and no other element/elements. So, as bromine is not included in this group, this explanation is out of the question.
-Induced dipole-dipole interactions is when we see this uneven sharing of the electrons sitting between the atoms in a molecule due to some other nearby molecule creating a dipole. But, as the dipole in ICl is caused by the relative electronegativities of the atoms themselves in the molecule, and not necessarily be some external factors, then this shouldn't be the reason as to why it has a higher boiling point.

Hope that helps you out! :)