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Boiling Points

Posted: Sat Nov 09, 2019 12:36 am
by Ryan Chang 1C
Explain the difference in the boiling points of AsF3 (63 degrees C) and AsF5 (-53 degrees C).

I'm trying to understand this problem. Why does AsF3 have a higher boiling point? I thought that more electrons means a higher boiling point.

Re: Boiling Points

Posted: Sat Nov 09, 2019 9:31 am
by Ally Huang- 1F
If you draw the lewis structure for each compound, it makes this problem a little easier to understand. AsF3 has a lone pair on As, so it is polar and has dipole moments. Therefore, it will experience dipole- dipole interactions between molecules. AsF5 has no lone pairs on As and the dipole moments cancel each other out, making it non polar. AsF5 will not experience dipole- dipole interactions between molecules because it is non polar. The molecule with dipole- dipole interactions, AsF3, will have a lot higher boiling point, compared to a molecule without dipole-dipole interactions.

Re: Boiling Points

Posted: Sat Nov 09, 2019 11:50 am
by sarahwu3a
Yes, usually more electrons makes stronger bonds but in this case AsF3 has a long pair compared to AsF5 with no lone pairs. This gives the molecule a strong negative dipole and as a result the molecule has both london and dipole-dipole IMF.

Re: Boiling Points

Posted: Sat Nov 09, 2019 2:20 pm
by Arianna Perea 3H
why do boiling points play a role in the forces?

Re: Boiling Points

Posted: Sat Nov 09, 2019 2:44 pm
by 805097738
because molecules with dipole-dipole reactions have higher boiling points

Re: Boiling Points

Posted: Sat Nov 09, 2019 2:44 pm
by Trinity Vu 1D
Arianna Perea 3H wrote:why do boiling points play a role in the forces?
Its the other way around. Forces play a role in determining boiling points because different forces have different strengths and thus require more or less energy to break. AsF3 has a higher boiling point because it has dipole-dipole forces while AsF5 only has London forces. Dipole-dipole forces are stronger than London forces and therefore require more energy to break thus requiring a higher boiling point.

Re: Boiling Points

Posted: Sat Nov 09, 2019 4:48 pm
by faithkim1L
When you draw the lewis structure for both AsF3 and AsF5, the former has a lone pair of electrons over As. This results in polarity, and there are dipole-dipole moments in the molecule. However, in AsF5, there are no lone pairs on As, meaning that the whole molecule is nonpolar and has no dipole-dipole interactions. Because of this, AsF3 will have a higher boiling point compared to AsF5.