Polarity vs Non-Polarity

[Alejandra Reyna 1E]

Could someone help me understand how Lewis structures help in determining polarity? I've noticed there are arrows that either point towards or away from the central atom but I do not understand why. Thank you!

[Chem_Mod]

By looking at the Lewis structure one can see the atom connectivity.

Then, for each bond, using trends in electronegativity determine which atom pulls the shared electrons towards it. This unequal charge sharing creates a dipole between the pair of bonded atoms. This is what the line represents: the arrow pointing towards the more negatively charged atom.

Based on the Lewis structure and shape one can then tell if these dipole moments cancel (equal lines pointing away or towards each other).
If they cancel, the molecule is non-polar.
If they don't cancel, the molecule is polar.

Ask me after class or come to my office hours.
I have answered questions after every lecture for the entire class.

Also ask about this in the Peer Learning sessions and TA office hours.

[Wenxin Fan 1J]

Based on Lewis structures you can see the arrangement if atoms in reference to each other. Looking at the bonding between atoms in the structure can also be used to determine the 3d structure of the molecule. These characteristics can be used to determine polarity by using the VSEPR theory in conjunction with lewis dot diagrams.

[Sonja Kobayashi 1H]

Expanding on the other responses, you can look for symmetry for the molecule, meaning that if there are unequal sharing of electrons but in opposite directions, the polarity will cancel out. It is important to remember that unpaired electrons repel other bonds so it is best to compare electronegativity.