3F.5

[Annie Ye]

Suggest, giving reasons, which substance in each of the fol- lowing pairs is likely to have the higher normal melting point (Lewis structures may help your arguments): (a) HCl or NaCl; (b) C2H5OC2H5 (diethyl ether) or C4H9OH (butanol); (c) CHI3 or CHF3; (d) C2H4 or CH3OH.

[christabellej 1F]

To find which has a higher melting point, you would want to find out what types of IMFs each molecule or compound has, and determine which compound has the stronger IMF. For example, in a) HCl is a covalently bonded molecule while NaCl is an ionic compound. NaCl will have a higher melting point because its electrostatic attractions are stronger. In b) butanol would have a higher melting point than diethyl ether because butanol has H bonds, which are stronger than the IMFs in diethyl ether.

[Amy Luu 2G]

How do you determine that buthanol has h-bonds? How come diethyl ether doesn't have h bonds?

[Ashley Osorio]

Yeah, doesn't ether also have H bonds? They're bonded to the carbon just as in Butanol, so what's the difference? Is it because unlike in Ether, theres a carbon bonded to an Oxygen? If so, why is this important??

[Jared Khoo 1G]

Yeah, doesn't ether also have H bonds? They're bonded to the carbon just as in Butanol, so what's the difference? Is it because unlike in Ether, theres a carbon bonded to an Oxygen? If so, why is this important??

I don't think so because the Hydrogen is not bonded to N, O, or F, therefore there are no hydrogen bonds formed as there isn't a partial positive on the hydrogen. In contrast, in the butanol, the H is bonded to an oxygen, so hydrogen bonds would form.

[Jared Khoo 1G]

How do you determine that buthanol has h-bonds? How come diethyl ether doesn't have h bonds?

H bonds form when H is bonded to N, O or F.

[Jared Khoo 1G]

To finish off this problem,

C. CHI3 will have a higher melting point because iodine is bigger than chlorine with more electrons and therefore higher IMFs.
D. Methanol will have a higher melting point because of the presence of Hydrogen bonds.