Homework Question 4.25

(Polar molecules, Non-polar molecules, etc.)

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Alan Chien 1J
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Joined: Fri Sep 25, 2015 3:00 am

Homework Question 4.25

Postby Alan Chien 1J » Sun Oct 25, 2015 3:07 pm

On question 25 (a) in the Chapter 4 HW, we are given the molecule CH2CL2. I drew out the molecule as a Carbon with 4 covalent bonds, which would lead me to believe that it is non polar (AX4). However, the answer key says that CH2CL2 is polar because of its dipole moments, which I understand. So, is determining the shape/geometry of the molecule not enough to determine the polarity? An AX4 VSPER should be tetrahedral and non polar right?

Sophia 3F
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Joined: Fri Sep 25, 2015 3:00 am

Re: Homework Question 4.25

Postby Sophia 3F » Sun Oct 25, 2015 3:21 pm

I also have the same question. I understand why the molecule is polar because of its dipole moments in the Lewis structure the way its drawn in the solutions manual, but how do we know to draw the chlorides on the same side of the carbon instead of opposite sides? And if the chlorides are drawn on opposite sides then wouldn't the moments cancel out?

Janae Yip 3G
Posts: 15
Joined: Fri Sep 25, 2015 3:00 am

Re: Homework Question 4.25

Postby Janae Yip 3G » Sun Oct 25, 2015 10:51 pm

I read online that it is helpful to know that CH2Cl2 is widely used as a solvent (thus, it is a liquid.) If we know that this molecule is a liquid, then it must mean the elements are held together by some time of bond. Most often, because of this, there will be polarity.

Ronald Yang 2F
Posts: 86
Joined: Fri Sep 25, 2015 3:00 am

Re: Homework Question 4.25

Postby Ronald Yang 2F » Mon Oct 26, 2015 8:45 pm

If you think about it, even if in the lewis structure the Cl's are opposite with regard to the Carbon or on the same side, they still are oriented as a Cl-C-Cl bond in reality. No matter how you place the Cl in a lewis structure, if you were to translate that into a tetrahedral 3D arrangement, the molecule would still exhibit polarity. In a lewis structure, the placement of the Cl's would not matter. However, how it's drawn in the lewis structure isn't how it is shaped in reality. Thus, when you want to look at a molecule's polarity, you should look at its 3D actual shape to better determine a molecule's polarity.


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