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Fluorine and Electronegativity

Posted: Thu Nov 15, 2018 3:12 am
by Meachelle_Lum_1I
Which will have a higher melting point: CHI3 or CHF3?
I assumed it was CHF3 since Fluorine is the most electronegative and will have a strong pull on the electrons of the other atoms. Can someone explain why CHI3 is higher?
(6th edition 6.5c)

Re: Fluorine and Electronegativity

Posted: Thu Nov 15, 2018 9:29 am
by Courtney Quan 1C
Iodine is a larger atom and therefore has more electrons than fluorine does. Because of iodine's greater number of electrons, there is a better likelihood/tendency of electron fluctuations to occur and create a dipole (greater polarizability). This greater likelihood of electron fluctuations/shifts strengthens the dipole of iodine and results in a stronger intermolecular force than that of fluorine because a dipole is more likely to occur. Stronger intermolecular forces require more energy to break, which is why CHI3 has a higher melting point than CHF3.

Re: Fluorine and Electronegativity

Posted: Thu Nov 15, 2018 10:43 am
by Max Hayama 4K
Although fluorine has a larger electronegativity than iodine, there is still a covalent bond between the carbon and the fluorine so their is no permanent dipole between the two. As a result, iodine has a lot more electrons than fluorine, making it more polarizable thus resulting in greater induced dipoles between this bond. The greater the dipole moment, the more intermolecular forces.