Textbook Question 3F.15

[Adam_Ventura_1H]

I doo not really understand why AsF3 has a higher boiling point. At first instant I thought AsF5 would have a higher boiling point because it would have more electrons so it would have a stronger dispersion force.

Question: Explain the difference in the boiling points of AsF3 (63°C) and AsF5 (-53°C).

[Selena Quispe 2I]

AsF3 would have a higher boiling point than AsF5 because it is a polar molecule that has Dipole-Dipole and LDF. AsF5 only experiences LDF because all of the Fluorines are pulling it equally.

[Tam Nguyen 2B]

The main reason why AsF3 has a higher boiling point than AsF5 is because AsF3 has dipole-dipole IMFs due to the bonds being covalent. Whereas AsF5 has only London Dispersion IMFS because it is a nonpolar molecule. If you draw it out you'd be able to kind of tell the molecular shape and derive the kinds of bonds they have. Since dipole-dipole bonds are stronger than London Dispersion, the AsF3 has a higher boiling point than AsF5.

[Isabella Chou 1A]

To add on to the previous responses, when you draw the Lewis structure of AsF3, you will notice that As, the central atom, has two lone pair electrons. This lone pair is the reason why AsF3 is a polar molecule. The lone pair creates a net dipole moment in the molecule, so we know that AsF3 has dipole-dipole interactions.

[Angel More 2J]

AsF3 would have a higher boiling point than AsF5 because it is a polar molecule that has Dipole-Dipole and LDF. AsF5 only experiences LDF because all of the Fluorines are pulling it equally.

Could you please walk me through how you realized that AsF5 is a polar molecule?

[Selena Quispe 2I]

AsF3 would have a higher boiling point than AsF5 because it is a polar molecule that has Dipole-Dipole and LDF. AsF5 only experiences LDF because all of the Fluorines are pulling it equally.

Could you please walk me through how you realized that AsF5 is a polar molecule?

Hey! Sorry AsF3 is the polar molecule, because it has a lone pair! And if it is a polar molecule then it experiences dipole-dipole and Dipole Induced- Dipole Forces! I'm sorry if I confused you in the previous post :(

[Angel More 2J]

AsF3 would have a higher boiling point than AsF5 because it is a polar molecule that has Dipole-Dipole and LDF. AsF5 only experiences LDF because all of the Fluorines are pulling it equally.

Could you please walk me through how you realized that AsF5 is a polar molecule?

Hey! Sorry AsF3 is the polar molecule, because it has a lone pair! And if it is a polar molecule then it experiences dipole-dipole and Dipole Induced- Dipole Forces! I'm sorry if I confused you in the previous post :(

Ohhh got it! Thank you so much!

[Melanie Lin 3E]

Since As has 5 valence electrons, it perfectly bonds to the 5 F atoms and leaves no lone pairs, making it a nonpolar molecule. With AsF3, a lone pair is left on the As atom, so the molecule becomes nonpolar. With nonpolar molecules, the IMFs are much stronger than with nonpolar ones so the boiling point becomes higher.

[Tiao Tan 3C]

AsF3 has a higher boiling point because it has both dipole-dipole and LDF, while AsF5 only has LDF.
AsF3 is a trigonal pyramidal shape while AsF5 is tribgonal bipyramidal (symmetrical).
Therefore, dipole moments of AsF3 do not cancel, making it a polar molecule.