polar vs nonpolar

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

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Sarah Blake-2I
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Joined: Fri Aug 30, 2019 12:16 am

polar vs nonpolar

Postby Sarah Blake-2I » Sat Nov 16, 2019 3:31 pm

How can you predict based on looking at the molecular formula for a compound whether it is polar or nonpolar?

Jada Brown 2H
Posts: 100
Joined: Sat Aug 17, 2019 12:15 am

Re: polar vs nonpolar

Postby Jada Brown 2H » Sat Nov 16, 2019 3:47 pm

usually it is best to always draw the lewis structure, unless it is a vary simple compound, in which case you might be able to tell by looking at the formula. but in general i would say always draw it out just to make sure.

Sally Qiu 2E
Posts: 105
Joined: Fri Aug 30, 2019 12:18 am

Re: polar vs nonpolar

Postby Sally Qiu 2E » Sat Nov 16, 2019 3:59 pm

i prefer to draw the lewis structure; then you can see if the structure is symmetrical or not.

Posts: 50
Joined: Fri Aug 30, 2019 12:18 am

Re: polar vs nonpolar

Postby AnnikaMittelhauser4E » Sat Nov 16, 2019 4:09 pm

You really can't tell just from the formula unless it's something really simple like a diatomic molecule (H2, O2, etc are always non polar because their only bond is non polar).

Additionally, Lewis structures can be helpful, but they can also be misleading. For example, you could draw the Lewis structure of water as H-O-H with the lone pairs over the O. That may make the molecule seem linear and therefore non polar (if it were linear, the dipole moments formed by the polar H-O bonds would cancel). But, because of VSEPR, we know it's actually bent/angular and polar because the dipole moments don't cancel.

So, I think the best course of action is to memorize which molecular structures are generally polar vs non-polar and figure out the structure of any molecule you're given. Figure 2E.7 in the textbook is very helpful.

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Joined: Sat Jul 20, 2019 12:17 am

Re: polar vs nonpolar

Postby EthanPham_1G » Sat Nov 16, 2019 4:14 pm

In lecture, Lavelle spoke about how you can tell if a molecule is polar or non-polar if it has polar or non-polar bonds. Polar bonds have an electronegativity difference between the two atoms and non-polar bonds do not have an electronegativity difference. If there are polar bonds, the molecule can still be non-polar if the dipole moments cancel. I guess the best way to tell if a molecule is polar or nonpolar by looking at it is to draw its Lewis structure and its VSEPR shape so that you can tell if the bonds are polar or non-polar and to see if the dipole moments cancel.

Aarushi Solanki 4F
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Joined: Sat Jul 20, 2019 12:17 am

Re: polar vs nonpolar

Postby Aarushi Solanki 4F » Sat Nov 16, 2019 4:17 pm

You usually cannot simply look at the molecular formula and determine its polarity. It's important to look at the lewis structure, and even the molecular shape. For example, the lewis structure for CH2Cl2 seems symmetrical from a 2-D perspective; however, because it is tetrahedral, the dipoles don't actually point in opposite directions (3-D perspective).

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Joined: Wed Sep 11, 2019 12:15 am

Re: polar vs nonpolar

Postby HuyHa_2H » Sat Nov 16, 2019 5:12 pm

Generally, you can't really determine polarity just off of the molecular formula which is why you use the VSEPR models to determine it as it is the actual accurate representation of the molecule.

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