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polar or non polar?

Posted: Sat Nov 16, 2019 9:18 pm
by Doris Cho 1D
how can you tell if a molecule is nonpolar or polar based on its lewis structure? or can you only tell from the difference in electronegativity?

Re: polar or non polar?

Posted: Sat Nov 16, 2019 9:21 pm
by Alex Tchekanov Dis 2k
Polarity is a combination of the molecular geometry and the electronegativity. For example, a linear molecule such as BeH2 is not polar because the central atom has two atoms of equal electronegativity on either side and the dipole moments cancel each other out. However for a linear molecule such as HCN, because N is more electronegative than H, the molecule is polar because the net dipole moment is not canceled out. This can be applied to all molecular shapes. Therefore, it is very important to not just consider the lewis dot but also the geometry.

Re: polar or non polar?

Posted: Sat Nov 16, 2019 9:23 pm
by Nicholas_Gladkov_2J
Doris Cho 1D wrote:how can you tell if a molecule is nonpolar or polar based on its lewis structure? or can you only tell from the difference in electronegativity?


You would use both the lewis structure and the electronegativity to tell if the molecule is polar or non-polar. For example, in class when Dr. Lavelle showed us dichloroethene, depending on the lewis structure (cis, or trans dichloroethene) the molecule is polar or non-polar.

Re: polar or non polar?

Posted: Sat Nov 16, 2019 9:50 pm
by preyasikumar_2L
You can somewhat tell whether molecules are polar or nonpolar by whether or not their Lewis structures are symmetrical or not. Symmetrical = nonpolar, asymmetrical = polar (in general)

Polar molecules must have polar bonds (bond between two different elements) with dipoles that do not cancel. Non-polar molecules must have a net total of zero electric dipole moments which is possible if it contains non polar bonds (bond between two of same element) or polar bonds with dipoles that cancel.

Re: polar or non polar?

Posted: Sat Nov 16, 2019 9:59 pm
by stephaniekim2K
You need both to figure out if it is polar/nonpolar. Electronegativity will tell where the pull of electrons is, but the Lewis structure shows the positioning of the atoms and whether they will cancel or not.

Re: polar or non polar?

Posted: Sat Nov 16, 2019 10:47 pm
by Janet Nguy 2C
You can tell from the Lewis structure if a molecule is polar or nonpolar by looking at the dipole moments (which you can discern using electronegativity trends). If they cancel (meaning the dipole moments point in opposite directions) then it will be nonpolar. Additionally, a molecule will be nonpolar if it doesn't have dipole moments at all. If the dipole moments do not cancel, it would be considered a polar molecule.

Re: polar or non polar?

Posted: Sat Nov 16, 2019 11:27 pm
by Catherine Daye 1L
You can kind of think polarity as "unevenness" because electrons are unevenly distributed. Therefore, you can look at how symmetrical a lewis structure is to determine it's polarity. If it is completely symmetrical, then it is most likely nonpolar. If it is not, then it is polar with a side containing more electrons.

Re: polar or non polar?

Posted: Sun Nov 17, 2019 12:31 am
by MBouwman_4A
In order to determine if the molecule is polar or non-polar, you would use the electronegativity of the atoms as well as the Lewis structure. The electronegativity would show you the charges of the bonds and the Lewis structure would show you if the dipoles cancel.