Welcome Guest Search | Active Topics |

Tag as favorite
AAMC Chemistry Practice Set Q.72
Options
Previous Topic Next Topic
Anastasia_6156
#1 Posted : Monday, May 17, 2021 9:54:38 PM
Rank: Newbie

Groups: Registered
Joined: 5/8/2021
Posts: 1

Thanks: 0 times
Was thanked: 0 time(s) in 0 post(s)
Question 72 asks about the least polar compound. I do not understand why is it CBr4 - I don't think it was on a lecture?..
Back to top
Report?
Youssef_6546
#2 Posted : Tuesday, May 18, 2021 5:18:12 AM
Rank: Member

Groups: Registered
Joined: 4/28/2021
Posts: 15

Thanks: 0 times
Was thanked: 0 time(s) in 0 post(s)
Hi Anastasia,

For question 72, AAMC is assessing our understanding of polariity and what makes a compound more polar than the other. Yes, we didn’t specifically discuss CBr4 in lecture, but we did learn how to determine a compound’s polarity based on the net dipole of the compound’s atoms (page 51 of ChemOchem Class Companion). CBr4 has a tetrahedral shape like CCl4 (as shown in page 51). With this shape, the individual dipoles cancel out which gives a net dipole moment of zero. Hence CBr4 is non-polar and the least polar among the other three options in the question

Hope these help!
Back to top
Report?
INSTR_Katrina_128
#3 Posted : Thursday, May 20, 2021 10:18:32 PM
Rank: Advanced Member

Groups: Registered
Joined: 5/18/2021
Posts: 73

Thanks: 0 times
Was thanked: 0 time(s) in 0 post(s)
Great explanation, Youssef!

I want to mention that the OVERALL polarity of the molecule CBr4 is 0.

However, each bond of C---Br is (slightly) polar.

What's the difference or distinction in these statements?

Stretch your two arms out beside you, and imagine that you have two friends (wow... friends... remember those? 😥) tugging on your arms. If they are both EQUALLY strong, you will feel an equal-and-opposite balanced force on your arms, and you won't move anywhere. This is what C-Br4 feels. It has FOUR ARMS, and feels an equal and opposite force in 4 different directions. It's not moving anywhere (i.e., it's not a polar molecule), but each of its individual arms FEELS a pulling force, so each individual ARM is (slightly) polar.

I say *slightly* polar because the electronegativity difference (a way that we can quantify polarity) between C and Br is small (about 0.3).
Back to top
Report?
Users browsing this topic
Guest (3)
Tag as favorite
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.

Clean Slate theme by Jaben Cargman (Tiny Gecko)
Powered by YAF | YAF © 2003-2009, Yet Another Forum.NET
This page was generated in 0.087 seconds.