polarity vs. nonpolarity

[josephyim1L]

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]

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]

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]

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]

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]

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]

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]

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]

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.