polar or non polar?

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

Doris Cho 1D
Posts: 53
Joined: Thu Jul 11, 2019 12:16 am

polar or non polar?

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?

Alex Tchekanov Dis 2k
Posts: 118
Joined: Sat Aug 24, 2019 12:16 am

Re: polar or non polar?

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.

Posts: 125
Joined: Sat Aug 17, 2019 12:17 am

Re: polar or non polar?

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.

preyasikumar_2L
Posts: 101
Joined: Fri Aug 09, 2019 12:17 am

Re: polar or non polar?

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.

stephaniekim2K
Posts: 79
Joined: Fri Aug 09, 2019 12:16 am

Re: polar or non polar?

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.

Janet Nguy 2C
Posts: 115
Joined: Sat Aug 24, 2019 12:17 am

Re: polar or non polar?

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.

Catherine Daye 1L
Posts: 104
Joined: Wed Sep 11, 2019 12:16 am

Re: polar or non polar?

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.

MBouwman_4A
Posts: 40
Joined: Wed Sep 18, 2019 12:21 am

Re: polar or non polar?

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.