3F19 Part C

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Anisha Chandra 1K
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Joined: Thu Jul 11, 2019 12:17 am

3F19 Part C

Postby Anisha Chandra 1K » Wed Nov 20, 2019 10:59 am

The boiling point of pentane - CH3(CH2)3 CH3 is 36.1 C, whereas that of C(CH3)4 is 9.5C.

The solutions say that pentane has a higher surface area and thus stronger London forces than C(CH3)4 because C(CH3)4 is spherical and more compact, but how do you draw the lewis structure of C(CH3)4 to determine that it is more compact? The way I drew it, C(CH3)4 seemed longer, more linear, and less compact...

sarahforman_Dis2I
Posts: 109
Joined: Sat Aug 17, 2019 12:18 am

Re: 3F19 Part C

Postby sarahforman_Dis2I » Wed Nov 20, 2019 12:44 pm

Anisha Chandra 4H wrote:The boiling point of pentane - CH3(CH2)3 CH3 is 36.1 C, whereas that of C(CH3)4 is 9.5C.

The solutions say that pentane has a higher surface area and thus stronger London forces than C(CH3)4 because C(CH3)4 is spherical and more compact, but how do you draw the lewis structure of C(CH3)4 to determine that it is more compact? The way I drew it, C(CH3)4 seemed longer, more linear, and less compact...



C(CH3)4 is drawn in a different way than CH3(CH2)3 CH3. C(CH3)4 is drawn with a C atom in the center. This carbon atom is bonded to 4 other carbon atoms. Bonded to each of those carbon atoms are 3 hydrogen atoms. This means that C(CH3)4 is NOT linear. In fact, the 4 C-C bonds form a tetrahedral shape. When one compares the shape of C(CH3)4 to CH3(CH2)3 CH3, it can be seen that CH3(CH2)3 CH3 is linear. Although the two molecules have the same molar mass, since CH3(CH2)3 CH3 is linear, it is more stackable, meaning that there is a higher surface area and higher LD forces.

Alexa Mugol 3I
Posts: 54
Joined: Sat Aug 17, 2019 12:17 am

Re: 3F19 Part C

Postby Alexa Mugol 3I » Wed Nov 20, 2019 4:22 pm

This image helped me in this question:
Image
Since they write neopentane as C(CH3)4, you would put a C in the center and bond it to four other Cs. So in a way, the textbook tries to help you out with the structure by writing the formula in a way that corresponds to its structure.


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