polarity
Moderators: Chem_Mod, Chem_Admin
-
- Posts: 46
- Joined: Wed Sep 18, 2019 12:21 am
polarity
why are some molecules that are symmetrical (like CH2Cl2) polar? shouldn't the symmetry mean that the dipoles can cancel?
-
- Posts: 149
- Joined: Sat Sep 14, 2019 12:17 am
Re: polarity
CH2Cl2 is a tetrahedral molecule, and tetrahedral molecules are only nonpolar if all bonded atoms are the same. The Cl pair is causing polarity to one direction and there isn't another opposing Cl pair.
-
- Posts: 51
- Joined: Sat Sep 14, 2019 12:15 am
- Been upvoted: 1 time
Re: polarity
I was really confused about this too, but I highly recommend that you watch this Youtube video to contextualize the answer:
https://www.youtube.com/watch?v=As-hcYY8Yaw
Start at the the 5 minute mark.
To give you a written answer, CH2Cl2 is polar because of the bond angles. Remember that a tetrahedral molecule has 109.5 degree bond angles. This means that every bond in CH2Cl2 is not directly across from each other. If the bonds were directly across from each other, the bond angles would be 180 degrees, but we know that's not the case. Since the bond angles are 109.5 degrees, there is no way for the two Cl atoms to be perfectly across from each other. They are always going to be angled in near each other. Because they are NOT DIRECTLY across from each other, the Cl bonds have dipole moments that do NOT cancel each other out. Look at the a picture of a tetrahedral molecule. You'll see that the bonds are all angles towards each other in some way.
https://www.youtube.com/watch?v=As-hcYY8Yaw
Start at the the 5 minute mark.
To give you a written answer, CH2Cl2 is polar because of the bond angles. Remember that a tetrahedral molecule has 109.5 degree bond angles. This means that every bond in CH2Cl2 is not directly across from each other. If the bonds were directly across from each other, the bond angles would be 180 degrees, but we know that's not the case. Since the bond angles are 109.5 degrees, there is no way for the two Cl atoms to be perfectly across from each other. They are always going to be angled in near each other. Because they are NOT DIRECTLY across from each other, the Cl bonds have dipole moments that do NOT cancel each other out. Look at the a picture of a tetrahedral molecule. You'll see that the bonds are all angles towards each other in some way.
-
- Posts: 110
- Joined: Sat Aug 24, 2019 12:17 am
Re: polarity
For a tetrahedral shape, the only time it is non polar is when all 4 of the bonded atoms are the same.
Re: polarity
Even though a tetrahedral shape is non polar because there are different atoms bonded on each side of the central atom there will be dipoles. And because the dipoles are unequal they will not cancel each other out and therefore it will be a polar molecule.
-
- Posts: 100
- Joined: Sat Aug 17, 2019 12:16 am
- Been upvoted: 2 times
Re: polarity
How do you know if they Cl atoms are across from each other or each across from a hydrogen atom when drawing the Lewis structure? Wouldn't this effect polarity?
Return to “Determining Molecular Shape (VSEPR)”
Who is online
Users browsing this forum: No registered users and 14 guests