Textbook question

[805377003]

3F.15 Explain the difference in the boiling points of AsF 3 ( 63 ) °C and AsF 5 ( − 53 ) °C.
Can someone explain this?

[Taylor K 2D]

The lewis structure of AsF3 reveals that there is one lone pair on the central atom, As, with three single bonds. This shows that AsF3 is a polar molecule (its not symmetrical and there is a clear dipole). AsF5, on the other hand, is nonpolar, as revealed by its symmetrical lewis structure. Polar molecules have stronger bonds than non polar molecules, and thus are harder to melt. This difference in polarity accounts for the difference in melting points.

[Nayra Gharpetian 3F]

Since AsF3 is polar, the bonds are stronger meaning it would require more energy to break the bonds. Therefore it would require a greater melting point compared to a non polar molecule like AsF5

[LarisaAssadourian2K]

Hello! When you draw the Lewis structures for both molecules, you will notice that AsF3 has a lone pair of electrons. This makes it a polar molecule, leading to it having stronger bonds and a higher boiling point. I hope this helps!