Polar vs. Nonpolar

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Emma Randolph 1J
Posts: 65
Joined: Fri Sep 28, 2018 12:29 am

Polar vs. Nonpolar

Postby Emma Randolph 1J » Fri Nov 16, 2018 10:42 am

I'm still confused how to tell if a molecule is polar or nonpolar/ how to know which atom has the delta negative or delta positive charge. Is there a way you can tell which atom has the positive or negative charge by looking at the periodic table or something?

Raymond Ko 1H
Posts: 29
Joined: Fri Sep 28, 2018 12:19 am

Re: Polar vs. Nonpolar

Postby Raymond Ko 1H » Fri Nov 16, 2018 11:06 am

You can tell which atom in the molecule has the delta negative or delta positive charge by determining which atom is more electronegative. Based on the periodic trends we learned for electronegativity, you can determine which molecules would attract a bonding pair of electrons more. The more electronegative atom attracts the electrons more, giving it the delta negative charge.

Faith Fredlund 1H
Posts: 68
Joined: Fri Sep 28, 2018 12:18 am

Re: Polar vs. Nonpolar

Postby Faith Fredlund 1H » Fri Nov 16, 2018 11:35 am

Determining whether a molecule is polar or nonpolar requires a combination of knowledge of an element's electronegativity (which can be seen through trends on the periodic table) and an understanding of the shape of the molecule. For a molecule to be polar, is must have dipole moments-- at which atoms have differing electronegativities-- that do not cancel. For a molecule to be nonpolar, there must be zero dipole moments (i.e., the atoms have the same electronegativity such as an H2 molecule), or if there are dipole moments, they must cancel. They cancel when they are arranged symmetrically around the central atom, as in a CH4 molecule.

SophiaKohlhoff4B
Posts: 30
Joined: Fri Sep 28, 2018 12:16 am

Re: Polar vs. Nonpolar

Postby SophiaKohlhoff4B » Sun Nov 18, 2018 11:04 pm

If dipole moments, caused by differences in electronegativity, do not cancel, then the molecule will be polar. The atom with the greater electronegativity will get the delta negative and the atom with the lower electronegativity will have the delta positive. Electronegativity follows the general trend on the periodic table of increasing from left to right and bottom to top.

Nicole Elhosni 2I
Posts: 62
Joined: Fri Sep 28, 2018 12:28 am

Re: Polar vs. Nonpolar

Postby Nicole Elhosni 2I » Mon Nov 19, 2018 7:55 am

Why is that in the CH2Cl2 molecule, the dipole moments of the chlorine atoms do not cancel out and result in a nonpolar molecule?

Cameron_Greenberg_3C
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

Re: Polar vs. Nonpolar

Postby Cameron_Greenberg_3C » Fri Nov 23, 2018 2:46 pm

It is based upon electronegativity, which is highest on the upper right of the periodic table. Non-polar molecules typically have a difference of 1.5 or less between the two atom's electronegativity values. Polar molecules typically have a 2.0 or greater difference. Symmetry and shape also play a part in determining polarity. If the molecule is symmetrical shape-wise with the same atoms on both sides, it is usually non-polar.


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