What has the higher normal melting point: CHI3 or CHF3?

The answer in the book is CHI3. So I'm assuming the answer is CHI3 because Iodine is the bigger and will form larger london dispersion forces, but isn't a stronger dipole moment formed in CHF3 because fluorine is more electronegative than carbon and forms a polar molecule?

Yes, your reasoning is correct. While CHF3 (fluorotrifluoromethane) has a stronger dipole moment due to the greater electronegativity difference between carbon and fluorine, CHI3 (iodoform) has a higher normal melting point. This is because the larger iodine atom in CHI3 allows for stronger London dispersion forces, which are the primary intermolecular forces in nonpolar molecules like CHI3. These dispersion forces increase with increasing molecular size, leading to a higher boiling point for CHI3 compared to CHF3.

To determine which compound, CHI3 or CHF3, has a higher normal melting point, we need to consider several factors.

First, let's examine the intermolecular forces present in each compound. CHI3 contains iodine, which is a relatively large atom. The larger the atom, the greater the number of electrons, and the larger the London dispersion forces, which are the weakest intermolecular forces. In CHF3, fluorine is more electronegative than carbon and forms polar covalent bonds. This creates a significant dipole moment within the molecule, leading to dipole-dipole interactions as additional intermolecular forces.

The strength of intermolecular forces plays a critical role in determining the melting point of a compound. Generally, compounds with stronger intermolecular forces have higher melting points.

In this case, while CHF3 forms polar molecules, CHI3 has both polar molecules due to the C-I bond and significant London dispersion forces due to the size of the iodine atom.

Now, let's address your question about the strength of the dipole moment in CHF3. Although CHF3 has a dipole moment, it is important to note that London dispersion forces also contribute to the overall intermolecular interactions.

When comparing CHF3 and CHI3, the dominant factor in determining the higher normal melting point is the strength of the London dispersion forces. Even though CHF3 has a dipole moment, the significantly larger London dispersion forces in CHI3, due to the larger size of iodine, make it the compound with the higher normal melting point.

Therefore, the answer is CHI3.

Yes, CHF3 is more polar but the size trumps that. I looked up the boiling points of

CHF3 is about -82 C.
CHCl3 is about 61
CHBr3 is about 149
CHI3 is about 218

chcl3 kis ke liye hota hai