polarity vs. nonpolarity

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

Moderators: Chem_Mod, Chem_Admin

josephyim1L
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am

polarity vs. nonpolarity

Postby josephyim1L » Tue Nov 27, 2018 12:06 am

what's the easiest and most systematic way of determining if a molecular structure is polar/nonpolar? Do I have to look at the Lewis structure or know the VSEPR structure?

Meachelle_Lum_1I
Posts: 92
Joined: Fri Sep 28, 2018 12:24 am

Re: polarity vs. nonpolarity

Postby Meachelle_Lum_1I » Tue Nov 27, 2018 12:13 am

Drawing the Lewis Structure usually helps!
Once you draw the structure you can see if there is a net dipole moment - if there is one then it is polar.
A helpful tip though is that C bonded to H is always nonpolar.
Also, if the Lewis Structure is symmetric, it is usually nonpolar because the dipoles will cancel. If it's not symmetric, it's polar.
If the surrounding atoms around a central atom are all the same and the Lewis Structure is symmetric, it's nonpolar (ex: CH4)

Matthew Mar 1J
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am
Been upvoted: 1 time

Re: polarity vs. nonpolarity

Postby Matthew Mar 1J » Tue Nov 27, 2018 11:40 am

You do have to be careful when looking at dipole moments because some nonpolar molecules can have dipole moments, they just cancel out against other dipole moments. For a molecule to be polar it must have polar bonds with dipoles that don't cancel.
Professor Lavelle also said it would be helpful to do the quick test where you think of a positive point and consider whether or not there is any side of your molecule would be more attracted to that point (I think this method requires the VSEPR model, but it's really only necessary for more complex shapes).

Jeannine 1I
Posts: 73
Joined: Fri Sep 28, 2018 12:27 am

Re: polarity vs. nonpolarity

Postby Jeannine 1I » Tue Nov 27, 2018 1:18 pm

Matthew Mar 1J wrote:You do have to be careful when looking at dipole moments because some nonpolar molecules can have dipole moments, they just cancel out against other dipole moments. For a molecule to be polar it must have polar bonds with dipoles that don't cancel.
Professor Lavelle also said it would be helpful to do the quick test where you think of a positive point and consider whether or not there is any side of your molecule would be more attracted to that point (I think this method requires the VSEPR model, but it's really only necessary for more complex shapes).


Do all nonpolar molecules have dipole moments? And can there be dipole-dipole interactions in nonpolar molecules? This confuses me.

Catherine Kim 3K
Posts: 31
Joined: Fri Sep 28, 2018 12:26 am

Re: polarity vs. nonpolarity

Postby Catherine Kim 3K » Tue Nov 27, 2018 1:25 pm

You should first draw a Lewis structure. Then, there are multiple methods to see if the structure is polar or nonpolar. You should check the polarity of bonds, the electron groups around the central atom, and symmetry of the molecule.

905096106
Posts: 30
Joined: Fri Oct 05, 2018 12:17 am

Re: polarity vs. nonpolarity

Postby 905096106 » Tue Nov 27, 2018 1:31 pm

I would suggest first looking at the lewis structure and determining if it is symmetrical, this can be figured out by whether or not all the atoms surrounding the central atom are the same i.e. CCl4

Tyra Nguyen 4H
Posts: 74
Joined: Fri Sep 28, 2018 12:25 am

Re: polarity vs. nonpolarity

Postby Tyra Nguyen 4H » Tue Nov 27, 2018 4:33 pm

Meachelle_Lum_3C wrote:Drawing the Lewis Structure usually helps!
Once you draw the structure you can see if there is a net dipole moment - if there is one then it is polar.
A helpful tip though is that C bonded to H is always nonpolar.
Also, if the Lewis Structure is symmetric, it is usually nonpolar because the dipoles will cancel. If it's not symmetric, it's polar.
If the surrounding atoms around a central atom are all the same and the Lewis Structure is symmetric, it's nonpolar (ex: CH4)


How do you know that the C-H bond is nonpolar?

Dana Wilks 3I
Posts: 30
Joined: Fri Sep 28, 2018 12:23 am

Re: polarity vs. nonpolarity

Postby Dana Wilks 3I » Tue Nov 27, 2018 5:05 pm

905096106 wrote:I would suggest first looking at the lewis structure and determining if it is symmetrical, this can be figured out by whether or not all the atoms surrounding the central atom are the same i.e. CCl4


I am confused about whether you should be looking at the lewis structure or the molecular geometry, since lewis structures do not necessarily align with what the molecule looks like in reality.

Veronica Soliman 4H
Posts: 51
Joined: Fri Sep 28, 2018 12:28 am

Re: polarity vs. nonpolarity

Postby Veronica Soliman 4H » Tue Nov 27, 2018 6:16 pm

LOOK FOR THE DIPOLE MOMENT that doesn't cancel to 0. For example, hydrogen bonding is polar because it is a dipole-dipole interaction whereas weaker intermolecular forces like van der waals are nonpolar.


Return to “Determining Molecular Shape (VSEPR)”

Who is online

Users browsing this forum: No registered users and 2 guests