CHF3 vs CHI3 Melting Points  [ENDORSED]

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Riley_Yang_1J
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CHF3 vs CHI3 Melting Points

Postby Riley_Yang_1J » Mon Nov 11, 2024 11:57 am

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.

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Re: CHF3 vs CHI3 Melting Points  [ENDORSED]

Postby Chem_Mod » Mon Nov 11, 2024 11:09 pm

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.


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