Predict which compound from each of the following pairs will have the highest boiling points and why?

NH3, He, Ar, LiF

LiF-it is ionic

I agree with anonymous.

To predict which compound from each pair will have the highest boiling point, we need to consider the intermolecular forces acting between the molecules.

1. NH3 vs. He:
NH3 is ammonia, and He is helium. Ammonia is a polar molecule, meaning it has a partial positive and partial negative charge. Helium, on the other hand, is a noble gas and consists of nonpolar atoms. The intermolecular forces in NH3 are hydrogen bonding, whereas He only has weak van der Waals forces. Due to the stronger intermolecular forces in NH3, it will have a higher boiling point than He.

2. NH3 vs. Ar:
In this case, Ar is argon, which is a noble gas consisting of nonpolar atoms. Similar to the previous comparison, NH3 has stronger intermolecular forces due to hydrogen bonding, while Ar has weak van der Waals forces. Consequently, NH3 will have a higher boiling point than Ar.

3. NH3 vs. LiF:
LiF is lithium fluoride, and it is an ionic compound. NH3, again, has hydrogen bonding due to its polar nature. Ionic compounds like LiF have strong electrostatic forces between ions, known as ionic bonds. These forces are generally stronger than hydrogen bonding. Therefore, LiF will have a higher boiling point than NH3.

In summary, the compound with the highest boiling point in each pair would be NH3 compared to He and Ar. However, LiF will have a higher boiling point than NH3.