CHF3 vs CHI3 Melting Points [ENDORSED]

[Riley_Yang_1J]

Why does CHI3 have a larger melting point than CHF3? The manual says that CHI3 has stronger van der waals interactions because of its larger size, but I thought that because F has a larger electronegativity it would result in a stronger dipole moment, leading to stronger dipole-dipole interactions.

[Chem_Mod]

The dipole moment of C−Cl bond (1.86 Debye) in CH3−Cl is greater than dipole moment of C−F bond (1.85 Debye) in CH3−F.

This is why I covered this equation conceptually in class: dipole moment = q x d

You are omitting the longer bond length for C-I contributing to the magnitude of the dipole.

Iodine has many more electrons than fluorine and stronger van der Waals interactions.

Count the total electrons in CHI₃ versus CHF₃.