Textbook question 3F.5

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Aaina 2D
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Joined: Wed Sep 30, 2020 9:41 pm

Textbook question 3F.5

Postby Aaina 2D » Tue Nov 17, 2020 6:32 pm

Hi! In the homework question below, I don't understand why the answer is CHI3. Could someone please explain?

3F5 - Suggest, giving reasons, which substance in each of the following pairs is likely to have the higher normal melting point (Lewis structures may help your arguments): c) CHI3 or CHF3

Stuti Pradhan 2J
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Re: Textbook question 3F.5

Postby Stuti Pradhan 2J » Tue Nov 17, 2020 6:39 pm

From my understanding, since iodine has a larger atomic radius and therefore, its valence electrons are less tightly held, it is more polarizable. This will result in stronger LD forces between CHI3 molecules than CHF3 molecules, which require more energy to break and thus have a higher normal melting point.

Hope this helps!

Breanna Ouyang 1I
Posts: 92
Joined: Wed Sep 30, 2020 9:48 pm

Re: Textbook question 3F.5

Postby Breanna Ouyang 1I » Tue Nov 17, 2020 8:29 pm

I agree with Stuti! Both CHI3 and CHF3 are nonpolar molecules, which means the only intermolecular forces they experiences are LDFs. Once you know that, you figure out which of Iodine vs Fluorine is larger in size (and thereby more polarizable) to see which molecule has the stronger LDFs.


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